PART IV.—OSTEOLOGY.
[CHAPTER XXXVI.]
COLLECTING SKELETONS.
It is really strange that so few American collectors are taught the scientific value of skeletons, and the need to collect them, especially when in the haunts of rare animals. While hundreds of collectors gather bird skins by the cord, perhaps not one out of the whole lot saves a rough skeleton. Any one who is wholly unaccustomed to the preparation of skeletons is apt to stand appalled at the thought of preparing one from the beginning; and, indeed, the final work of cleaning and mounting is no child's play. But let me assure you that, so far as the field work is concerned, you can easily become a successful collector of skeletons of all kinds, even though you may never learn to clean and mount one. All you have to do in the field is to "rough out" skeletons from the flesh, and dry them in compact bundles for shipment.
A Rough Skeleton of a mammal, bird, reptile, or fish, is simply the complete bony framework of the body, from which the most of the flesh has been cut away with a common knife, after which the skeleton and remaining flesh has been dried preparatory to its being, at some indefinite time in the future, taken in hand by a professional osteologist. The work of preparation on such specimens is very simple, and when once learned is easily performed.
Selection of Specimens.—When a choice is possible, select large and perfect adult male specimens as subjects to be skeletonized. The skeletons of young animals are always imperfect in development, do not properly represent a species, and are seldom valuable except for comparison with other specimens of the same species. Very often a fine adult specimen has its skin so badly torn by shot or bullets, or the skin covering is in such a bad state of shedding, moulting, and the like, that the skin is totally unfit for preservation. In such a case the preservation of a fine perfect skeleton becomes a clear gain of one specimen to the collector and to science.
A perfect skeleton is one in which not a bone is missing, and in which no substitutions have been made. But it is by no means always possible to secure a wild animal without breaking some portion of its osteological anatomy. When a bone is broken, the best thing to do is to supply it with a corresponding bone from an animal of similar size and age. Sometimes the closet naturalist, who generally thinks that rare wild animals are gathered like berries, will grumble because a broken bone has thus been replaced, and find fault with the size of the substitute, but that need not trouble the collector's conscience in the least. I once shot a fine prong-horn antelope buck, skeletonized it carefully, cut up the skeleton, and carried the whole of it for three days attached to my saddle, while I rode a very restive and dangerous horse, and also carried two blankets and a Maynard rifle. That skeleton, thus earned, had some broken bones supplied from another specimen. It finally went to Europe, and fell into the hands of a closet naturalist, who blithely found fault with the collector because of the supplied bones. Again, when I once risked drowning in order to enter a cave on a dangerous sea-coast to collect guacharo birds, and got a goodly number, a German closet naturalist complained bitterly because a skin that was sent to him had two missing tail-feathers supplied by two other feathers that were a trifle smaller than the missing ones.
But I did once perform a feat in South America which filled the souls of my friends at Ward's with wonder, and even admiration. In collecting about half a dozen skeletons of capybara, each of which I took care should be absolutely perfect, by some brilliant man[oe]uvre I contrived to send home to the establishment one skeleton which was the happy possessor of two left forelegs and two left hind legs, but never a right one; and in the language of the Old Testament, "his bones are there to this day!"
Skeletons of Mammals: Small Objects.—The smallest quadrupeds—such as bats, small rodents, shrews, and the like—should be eviscerated, and preserved in alcohol, without being skinned; but each specimen should be fully labeled. As a general thing it is best, for various reasons, not to dry such small carcasses.
For all mammals below the size of the Virginia deer, proceed as follows:
1. Remove the skin as expeditiously as possible, in order to have a fair show at the skeleton.
2. If the skeleton is smaller than a fox, leave the legs attached to the body, for convenience, until you have cut the flesh away from them with your scalpel or pocket-knife, without any disjointing. When all the legs have been thus roughly denuded of flesh, cut them loose from the body and lay aside for the moment.
3. If the specimen is larger than a fox, cut off the legs from the body, lay each one flat upon the ground, inside uppermost, divide the flesh all the way along it directly over the bones, and literally dissect the bones out of the mass of flesh, instead of cutting the flesh away piece by piece. This is the quickest and neatest way. The scapula must come off with the fore leg, and be left attached to the humerus. Be sure you cut off all the masses of flesh, but don't cut off the knee-pan, as you may easily do if you are not watchful.
4. Now for the carcass. Hold it on its back, begin at the breastbone, flake off the flesh from the sides of the body close down to the ribs, until the backbone is reached. Cut off as much flesh as you can (hurriedly) from along the backbone.
5. Next attack the abdomen. Beginning at the lower point of the breastbone, detach the walls of the abdomen from the ends of the short ribs, down to the lumbar vertebræ, and so on around the iliac margin of the pelvis. Cut through the diaphragm close up to where it is attached to the ribs, and remove at one effort the entrails and vital organs.
6. Cut away the flesh from the pelvis, both inside and out, and the flesh of the tenderloin from underneath the lumbar vertebræ.
7. Cut the flesh from the thick portion of the tail.
8. Cut off the head at the first cervical vertebra, and clean the skull as previously described elsewhere, but leave the hyoid bone in its place.
9. Cut the flesh away from the neck vertebræ as well as you can. Be careful not to cut the sternum (or breastbone), which is soft cartilage, and easily cut; nor the ends of any vertebral processes, nor any soft bones.
10. If the skeleton is a small one, it is apt to get quite bloody during the operation. Wash it clean, and if necessary soak it in clear water for an hour or two. It will come all the whiter for it in the end. Skeletons of ruminant animals are generally clean enough without that.
11. Do not poison a rough skeleton with arsenical soap, nor put salt upon it; so says Mr. Lucas, the osteologist of the National Museum. The former has a tendency to prevent skeletons from properly macerating and coming white. Sprinkle dry arsenic upon a skeleton, if anything is necessary to protect it from Dermestes and other insects. Never put alum on a skeleton.
[a]Fig. 66.]—Rough Skeleton of a Small Animal. (After F.A. Lucas.)
12. The last thing is to make up the skeleton into a small, compact bundle, that will pack nicely and economically when dry, and withstand some pressure without breakage. Put the skull in the chest cavity. Fold up the upper joints of the legs, put the foot of each in the pelvis, and the other end in the cavity of the chest. Now tie all the legs tightly to the spinal column. (See Fig. 66.) Bend the tail under the pelvis and tie it fast also. Finally, hang the specimen up in the shade and wind, so that it will dry quickly.
It will be observed that the above process leaves the body of the skeleton entire, and all the bones of each leg and foot united by their natural ligaments. A skeleton prepared thus may ultimately be mounted as a "ligamentary skeleton," or it may be disjointed throughout, macerated, and mounted as a "disarticulate skeleton." Except for skeletons of bison, elk, and other animals which are entirely too large to admit of transporting their bodies whole, it is much the best to prepare all others in the field as described above, and disarticulate some of them afterward; for this reduces to a minimum the chance of losing some of the parts.
Skeletons of Large Mammals.—The process of roughing out the skeletons of large mammals, no matter how large they may be, is precisely the same as described above for small ones; but to make it possible to transport and box them, they must be cut to pieces, or, I had better say, disjointed, for fear some zealous partisan might interpret my words too literally, and go at a valuable skeleton with an axe. And right here let me publish a law which is as fixed and unalterable as the laws of the Medes and Persians, and admits of no exception:
In disarticulating a large skeleton, no matter how large, an axe or hatchet must never be used for any purpose whatever. Use nothing but the knife, and in a few cases a small saw to separate the sternum from the ends of the ribs.
To come down to the details of cutting up a large skeleton in, the field, and making it up into a number of separate bundles, let us suppose that the skeleton lies before us, completely roughed out, in accordance with previous advice. The bones of each leg must be dislocated (at the "knees" in ruminant animals) either once or twice, so that the parts can be easily handled. In a full-grown elephant the leg bones are so large it is necessary to cut the ligaments at each joint, so that the scapula, humerus, radius and ulna, and foot may each be handled separately.
Of course, the head is to be cut off at the first cervical vertebra. Then, by careful work, and much coaxing with the sharp point of the knife, dislocate the spinal column just where the neck joins the body. At first this will bother you, but have patience and you will soon learn how to do it easily and quickly. In dislocating the spinal column, take hold of the neck, move it backward and forward, and strain it a bit to see just where the articulating surfaces of the vertebral process are, so that you can cut them. When your intelligence has made some headway on the joint, then you may put forth a little main strength and tear the vertebræ apart, but do not attempt this too soon.
The next thing is to cut off the ribs, and the first step toward this is to cut out the sternum, or breastbone. (See Plate XX.) This so-called bone is really cartilage, soft enough in a fresh skeleton to cut on the outside, and in thin places, like cheese rind. It must be cut out in one piece, the same as may be seen in the figure of the mounted skeleton, and the dotted line A B shows where the cartilaginous ribs of the sternum join the bony ribs that form the main arch of the thorax. At the points marked by the dotted line, cut the two apart. I have never found it necessary to use a saw for this work in a perfectly fresh skeleton, but in dry ones a saw is necessary. When you come to the short, or "floating ribs," as they are called, it will be found that their cartilages are only attached weakly to the cartilages of the previous ribs, or else are altogether free. These must be cut from the ribs and preserved with great care.
After the ribs have been cut free from the sternum, separate them from the backbone, one by one, make them up into bundles, and tie them up. The pelvis is to be separated from the spinal column at the last lumbar vertebra; and if necessary the spinal column may be again dislocated about the middle.
Formerly it was my practice to poison all rough skeletons with a thin wash of arsenical soap, to make them dry without smelling badly, and to keep off the myriads of insects that the shreds of flesh would naturally attract. Now, however, in obedience to the mandates of Mr. Lucas, I have eschewed the use of arsenical soap for this purpose, and recommend the use of dry arsenic instead, which does not retard the cleaning of the bones.
Rough Skeletons of Birds.—As in the case of a small mammal, first remove the skin from the body; but if the identity of the bird is in doubt, leave the large tail feathers and the primaries in place, for future reference. In fact, it is a good plan to always leave the primaries and spurious quills on the wing, for then there will be no danger that some of the small bones of the last joint will get lost or cut away by mistake. Moreover, when you come to tie up the skeleton, the primaries will afford valuable protection to the ribs.
[a]Fig. 67.]—Rough Skeleton of a Bird. (After F.A. Lucas.)
With a bird, the entire skeleton should be roughed out before any disjointing is done, and even then none is necessary, save to cut off the legs of large birds, especially those with long legs. Study carefully the accompanying figure of a bird skeleton (Fig. 67), and then it will be hardly necessary to say more than to roughly, but carefully, cut off the flesh with a cartilage knife or scalpel, and remove all the viscera. Look out for those delicate little points on the neck vertebræ, and also be very careful not to cut off those curious little appendages (called uncinate processes) that project backward from the middle of each rib. Leave the hyoid bone in its place, and also the bony ring surrounding the eyeball of the great blue heron, the owl, and other birds of prey. If any portion of the windpipe reveals any bony structure, the entire windpipe should be saved. Whenever any tendons are found to be partly ossified, as they will certainly prove to be in the "drumstick" of your Thanksgiving turkey, leave them in place for the osteologist to do with as he pleases.
When in doubt about any special part, give the osteologist the benefit of the doubt by saving the special part for him.
If the bird is a large one, cut off the head, and after cleaning it pack it away in the chest cavity. If the bird is small, you can leave it attached to the neck, and remove the brain by bending the head down and cutting it half off from above, thus exposing the occipital opening at the back of the skull, through which the brain may be drawn out.
After the skeleton has been roughed out, it should always be cleaned by washing it in a basin of water and brushing it meanwhile with a soft tooth-brush. If blood is left on the skeleton, the bones will absorb it, and become permanently discolored thereby. The cleansing done, make the skeleton up into a compact bundle by folding the wings naturally against the body, bending the neck down in some way so that it can be tied upon the body, and either cutting off the legs and putting them into the thorax and pelvis, or leaving them on and folding them up as compactly as possible. Then tie the bundle up thoroughly by passing a light string many times around it, so that it can never lose its compactness. Sprinkle it with dry arsenic, or wash over with thin arsenical soap, and hang it up in the shade to dry.
Skeletons of Reptiles.—After all the foregoing directions, it surely is unnecessary to describe, in detail, the skeletonizing of reptiles. The principles are precisely the same as already set forth for birds and mammals. Wherever special bones or cartilages are found, as in the abdominal-cartilaginous ribs of crocodilians and certain lizards, they must be carefully saved whole and in situ. With large skeletons, take whatever means are necessary to get them, while fresh, into compact shape for drying and packing. With large crocodiles and alligators, the neck, legs, head, and tail all go nicely inside the body, as I have proved scores of times. The skeleton of a large serpent is easily done up in a close coil, by which it not only takes compact shape, but the ribs are well protected. With serpents, do not attempt to cut the flesh from between the ribs, for it is desirable that it should remain.
On each rib of a crocodilian there is a strange, flat piece of cartilage attached to the posterior edge at the middle of the rib, and projecting backward, quite overlapping the next rib, as sure as the world the reptilian development of what in the full-fledged bird becomes a bony uncinate process. You will soon discover this in skeletonizing your first crocodilian, and be sure to respect its anatomy.
It surely is superfluous to say that every skeleton must be carefully and fully labeled, and in a substantial way.
Fishes.—This subject has been treated in Chapter IX. (Collecting Fishes).
Skeletonizing Cetaceans.—The rough skeleton of a cetacean—porpoise, blackfish, whale, and the like—is the bloodiest, greasiest, nastiest specimen the collector ever has to prepare. Nevertheless, they are necessary evils, and fortunately their structure is so simple that their roughing out is not a difficult matter. The vertebral column terminates in a point, there being no bones in the flukes of the tail, or the dorsal fin. The best way to operate is to split the body open along the middle of the back all the way from head to tail, and carve the flesh away until you reach the vertebral column, and after that the ribs.
The vertebral column must be cut in two in two or more places, according to its size. Midway between the last pair of ribs and the tail, and underneath the vertebral column, lie two very useless and absurd little ossifications known as the pelvic bones. They are called pelvic bones because that happens to be a handy name. They bear about as much resemblance to a genuine pelvis as a cigarette does to a locomotive. They are so small that it takes an expert with a search-warrant to find them, and, for my part, I always consider their loss a real gain to the cause of science. Of course the scapula and flipper, the ribs and the sternum, must each in turn be cut away, cleaned as well as possible, and bundled up to go with the head and the three sections of the vertebral column.
Packing Skeletons.—All rough skeletons, skulls, etc. (as well as all skins) must be thoroughly dry when packed, or they will sweat, soften up, smell offensively, and spoil any dry skins, or other perishable objects that may be packed with them. Skeletons should always be packed in tight boxes, so that rats and mice cannot get into them and gnaw the small bones. Tie some soft material over the teeth of separate skulls to save them from getting broken. Put the largest skeletons and skulls at the bottom, and use hay, straw, or excelsior for filling. Of course the small and fragile specimens will be put in the protected corners and crevices between the larger objects, and, as before remarked, dry skeletons that have been made up into compact bundles will stand a very considerable amount of pressure without breaking.
Collecting Fossil Skeletons.—The vertebrate zoologist glories in the skeleton of almost any living species of vertebrate, but a fossil skeleton he fairly worships. The more of previous theories it upsets, the dearer it is. If it is a reptile with feathers on its tail, a bird with teeth, or a scientific what-is-it, as was the gigantic megatherium, it is simply canonized. Beware, then, red-handed hunter of living species, how you recklessly pass by a bit of bone protruding from a "cut bank" beside some stream, for you know not the day and the hour when you may touch elbows with His Mysterious Highness, the Missing Link.
The tertiary deposits of the United States contain the fossil remains of many magnificent vertebrates, impossible even to mention here. Very often huge bones and tusks of the mastodon are unearthed in well or ditch digging, and before they receive proper attention are exposed to the air and allowed to crumble into dust in a few hours. If a fossil bone is very soft when dug up, it will crumble in a short time unless properly cared for. If this is likely to be its fate, cover it up again without delay, to keep the air from it until you are ready to preserve it. To accomplish this, prepare a kettle of glue water (simply hot water with a little glue dissolved in it) and wrap the bone tightly from end to end with an abundance of twine. Then with a ladle or large spoon pour the glue water over the bone or tusk, gradually, but continuously, so that it will soak in, and when dry, it will bind together the weak material and form a hard shell of some thickness and protect the form of the bone intact. This will often save a fossil which would otherwise fall into countless tiny fragments in a few hours.
If a skeleton or portion thereof is embedded in a matrix of hard rock, do not attempt to work it out fully in the field. That is work for the laboratory—and a very good one at that, sometimes requiring costly tools, much skill, and plenty of time to chip away the surrounding rock.
Oftentimes the fossil remains of a fish, small reptile, or mammal are uncovered bodily by the removal of the slab of rock which has covered it for ages, like a blanket. In such cases do not attempt to pick the bones, one by one, out of their resting-place, but procure the necessary tools, cut out the entire slab of rock which contains the skeleton, and keep it in one piece forever. Such specimens have a good market value in cash, which will well repay the care and labor bestowed upon them; but at the same time a novice should not make the very common mistake of supposing that a fossil which is new to him must necessarily be worth its weight in gold. If you wish to sell any good fossils, you will get a fair valuation by offering them to Professor Henry A. Ward, Rochester, N.Y.
[CHAPTER XXXVII.]
CLEANING LARGE SKELETONS BY MACERATING.
There are two ways to clean the skeletons of large mammals: (1) by boiling the bones, and (2) by maceration. The first is short, cleanly, and agreeable; but the skeleton produced by it is sure to be full of grease, and is anything but white and pleasing to look upon when mounted. The boiling process is also detrimental to the texture of the bone. The professional osteologist, to whom a greasy bone in a mounted skeleton is an unpardonable offence, never thinks of boiling a skeleton to get the flesh off, for the reason that the grease is boiled into the bone instead of out of it. Cleaning by boiling is permissible only under exceptional circumstances. If you wish a particular skeleton for a special purpose within a very short time, or if you are so situated that macerating a skeleton is impossible then boiling is excusable, but steaming is far preferable.
Preparing a Skeleton for Maceration.—It is, of course, to be understood that it is only the skeletons that are too large to be scraped and mounted as "ligamentous skeletons" that are to be macerated, bleached, and afterward articulated with wire. The first thing to do is to cut out the sternum in one piece, as already shown in Plate XXI., poison it in arsenic water, and hang it away to dry and be scraped afterward. A sternum must never be macerated, for it is so soft the cartilaginous framework would be entirely destroyed. The skeleton must now be cut completely to pieces, excepting that it is not necessary to separate all the vertebræ of the spinal column. The ribs must be cut off, and the joints of the legs cut asunder. The large bones of the legs contain marrow, and of these bones each one must have a large hole drilled in each end on the face of the articulating surface, so that when mounted the holes will not show. These holes are to afford the water access to the interior of the bone.
Macerating and Cleaning.—The maceration of a skeleton is a question of time as compared with eternity. Procure a wooden barrel or keg large enough to contain the entire skeleton, knock the head out and see that there are no nails, nor any other metal anywhere on the inside to stain and discolor the bones. Pack the skeleton closely in the empty barrel, fill it up with water and let it stand. In a few days its offence, like Othello's, "is rank, and smells to heaven." But that is no matter, provided your barrel has no neighbors. Let it stand for four months, six months, a year, or two years if need be, until every particle of fleshy matter on the bones has disintegrated and become a pulp. Keep the barrel covered, and when the water evaporates and the bones on top are about to be exposed, fill up with water and keep the bones always covered. If a skeleton is very bloody, it is well to soak it for a week in salt water to dissolve the blood-corpuscles. Then it may be macerated as directed above. The odor will be horrible, but if you are going to study bones you must not mind that.
When you find upon examining the bones that the flesh has totally disappeared from them, leaving them dark-colored or even black, but without any fleshy matter upon them, they are then to be taken out. Pour off the water, place the entire contents of the barrel in a large sieve-bottomed tray, and wash the bones thoroughly. When that has been done, put them in a large tub of boiling water, and keep them in warm water while you scrape all the bones, one by one, with your bone-scraper, and scrub them with a stiff brush, going over the entire surface, and washing them meanwhile in the warm water. The interior of each of the large leg bones must be washed out with a strong syringe, and every cavity in the vertebræ must be carefully scraped out.
Bleaching.—Having carefully scraped and washed the bones, the entire skeleton is now to be soaked for a short time, the length of time varying according to the size and age of the skeleton, in a solution of chloride of lime and water. To make this of the proper strength, dissolve about two or three ounces of chloride of lime in a barrel of water. Bones of young or immature animals must not be left in this solution as long as those of old specimens. Young bones are soft and porous, and the chloride of lime will soon destroy them if they remain in it too long.
The following skeletons, adult in every case, require to be left in this solution a length of time as stated herewith: Dog, 6 hours; sheep, 6 hours; deer, 8; buffalo, 12; elephant, 12.
After removing the bones from this bath, wash them with clear water, lay them in slat-bottomed trays, with cheese-cloth above the slats, without piling one bone upon another, and expose them a number of days in the hot sun. After they have bleached on the upper side, turn them over. If it does not rain upon them occasionally, they should be sprinkled with water, late in the evening or early in the morning, to hasten the process.
Great care is necessary to keep the tiny carpal, tarsal, and phalangeal bones from getting lost. When the bones are white as chalk, or nearly so, tie the parts of each skeleton in a stout paper bag by itself, label it, and put it away until you are ready to mount it.
The sternum is to be soaked in clear water, with a little washing soda to cut the grease, until it is soft, and then scraped the same as the bones of a ligamentary skeleton, which process will be described in the next chapter.
[CHAPTER XXXVIII.]
CLEANING AND MOUNTING SMALL SKELETONS.
The skeletons of small vertebrates should never be macerated previous to mounting, for the reason that their complete rearticulation would be a practical impossibility. The bones must be left united at the joints by their natural ligaments, which when dry become quite hard, and with the aid of either one or two small brass standards will hold the entire skeleton erect and in proper shape. Skeletons mounted thus, with the parts attached to each other by their own dried ligaments instead of wires, are called ligamentous, or ligamentary, skeletons. All mammals smaller than a large fox, all birds smaller than a small ostrich, all turtles, lizards, iguanas, serpents, crocodilians, and all fishes are mounted in this way. Fortunately it is possible to clean to perfect whiteness the skeletons of almost all these subjects without putting them through the maceration process, which resolves everything into its component parts.
Drying before Mounting.—In order to have a skeleton so that it will scrape to the best advantage and become as white as possible, every ligamentary skeleton must be dried before it is finally cleaned and mounted. In a perfectly fresh skeleton the epiphyses and ligaments are so soft the operator would find it hard to keep from destroying them with his keen-edged steel scrapers, and the smaller bones and cartilaginous members would also be in great danger of mutilation in the same way. When a skeleton dries, all these soft portions harden, and when afterward the skeleton is soaked in clear water for two or three days, or longer as may be necessary, the flesh quickly softens so that you can scrape it all away without encroaching on the framework, and the ligaments at the joints are just soft enough that a portion of it may be scraped or trimmed away, and yet leave sufficient to hold each joint together.
Relaxing a Dry Skeleton.—As intimated above, this is accomplished simply by soaking the specimen in clear water until its joints are pliable, and the flesh upon the bones is soft enough to scrape off. In order that the specimen should not become offensive and disagreeable to work upon, it must not soak long enough for decomposition to set in, for that is the first stage of maceration. Therefore, scraping should begin just as soon as the flesh is soft enough to be readily removed.
[a]Fig. 68.]—Steel Bone-scrapers.
Scraping a Ligamentary Skeleton.—The removal of the flesh and other animal matter from a small skeleton is accomplished by scraping the bones with various chisel-edged scrapers specially designed for this work, and by clipping and trimming on the joints with either curve-pointed or straight scissors. The principles to be learned in skeleton-scraping are comparatively few and simple. In the first place, a sufficient quantity of the connecting ligament at each joint must be left to hold the two bones together in proper shape when the specimen dries. This must not be left in a thick, unsightly mass, but requires to be scraped and trimmed down so that it is reduced to as small a quantity as will serve the purpose. In scraping the flesh off the main stem of a bone, such as the humerus, for example, always begin at the end and scrape toward the middle. The skeletons of turtles, lizards, and the like are an exception to this rule by reason of their structure, and should be scraped from the middle toward each end. If you scrape from the middle of a mammalian or avian bone toward either end, before you are aware of it, you have loosened the attachment of the ligament, and have nothing left to hold the joint together. By beginning on the ligament itself, and working away from it, you can scrape it down so thin at the point of attachment that its identity is quite lost, and the point where it ends is hardly visible. This principle applies to the scraping of all ligamentary skeletons, except a few reptiles.
In cleaning bird skeletons beware of injuring the little tack like points which project downward from each of the cervical vertebræ. Have a care also for the soft bones of the coccyx, and the uncinate process which projects backward from the posterior edge of each rib. In fishes the greatest difficulty lies in leaving the ribs attached to the remainder of the skeleton, for if the operator is at all as the writer used to be in the days of his youth, he will be prone to scrape some of the ribs loose, and be obliged to glue them in place in the dry skeleton, with glue and cotton batting that has been clipped up finely with a sharp pair of scissors.
While a small skeleton is undergoing the scraping process it must not be allowed to get dry until it is finally set up in position. When the skeleton is not being worked upon, it must be kept soaking in clean water; but remember that this cannot go on very long, or maceration will set in, the ligaments will give way, and the bones will all come apart. A little borax in the water serves to arrest decomposition, and will allow a skeleton to remain soaking for several days longer than could otherwise be allowed. After a skeleton has been well scraped, in order to get it as white as possible and free from grease, it must be treated with
Javelle Water.
1/2 pound chloride of lime.
1 pound common washing soda.
1 gallon of boiling water.
Keep this on hand in a glass-stoppered jar, in the dark. In using it, draw off a small quantity in a broad, shallow, earthen dish. Lay every small skeleton in it, and with a soft tooth-brush of the right size, brush all the bones thoroughly for about five minutes. At the end of that process wash the skeleton thoroughly with clear water, and perhaps it is then ready to mount.
Often the bones of a small skeleton contain an inordinate amount of grease. The easiest and simplest way to remove it is to soak the greasy bones for several days or weeks, as may be necessary, in a jar of pure naphtha.
Mounting a Small Skeleton.—The skeleton of every bird, mammal, and reptile requires to have the spinal cord replaced by a stout zinc wire, to give both strength and rigidity to the structure. Zinc wire is necessary because iron wire will rust, and brass wire is too expensive to use when something cheaper and better is obtainable. If you cannot procure zinc wire, use good galvanized iron wire. For very large specimens you may use iron wire, but it must be covered with two coats of asphaltum, applied with a brush, like black paint. After inserting the wire the full length of the cavity of the spinal cord, leave enough of the end protruding beyond the first vertebra of the neck to afford a means for the attachment of the skull. The extra length to be allowed should always be nearly equal to the lateral depth of the brain cavity.
Attitude.—It is often somewhat difficult to decide upon the attitude the skeleton is to have when finished. The possibilities in this line are extensive, and the result depends entirely upon the character of the subject, and the knowledge and good taste of the operator. In the first place, the position of the skeleton must be a correct representation of some characteristic attitude of the species. For example, a sloth skeleton should hang underneath a branch; a monkey should be climbing, or walking on a stout bough; a hyena should sneak and crouch; a passerine bird should always perch, while the penguins and the auks must stand erect on flat pedestals. If the young osteologist can do so, it will pay him well to travel several hundred miles, if need be, to see the beautiful, and even elegant, collection of skeletons and other preparations in Mr. F.A. Lucas's Department of Comparative Anatomy in the National Museum, all of the specimens in which have been prepared, mounted and displayed by Mr. Lucas and his assistant, Mr. Joseph W. Schollick. I know of no other osteological collection which in the beauty and scientific accuracy of mounting, and exhibition arrangement of its specimens, can be considered equal to this. The museum-builder may well consider it a model of its kind. Every skeleton, from that of a tiny humming-bird to a whale forty-eight feet long, is as nearly perfect as human skill can make it, and the variety of the characteristic attitudes represented in the smaller species makes this collection a particularly attractive one.
PLATE XX.
[a]Ligamentary Skeleton (Domestic Cat).—Mounted and Drying.]
Process with Mammals.—We will assume that the skeleton has been carefully scraped, and is now ready for mounting. The successive steps in this work from start to finish are about as follows:
1. In case the skeleton has been dried after scraping, as is often done, it must be soaked in clear water until the ligaments are relaxed.
2. Cut a zinc or galvanized iron wire of the right length and size to replace the spinal marrow, and long enough that the upper end of it will project beyond the axis into the brain cavity of the skull. Sharpen one end of this wire so that you can force it well down into the sacrum, and insert it in its place in the spinal column.
3. Bend the vertebral column to its permanent shape. In doing this, draw the sternum well forward so that the ribs will spread out, and show a chest cavity of the right size for inflated lungs. If you are not careful in this regard, the chest cavity will be too narrow.
4. Hang the body in a frame made of light strips of wood, as shown in the accompanying plate. Let the body hang at just the right height from the pedestal to receive the legs (Plate XX.).
5. Space the ribs carefully by starting a thread from the neck, and taking a turn around each rib from the first to the last, finally making fast the remaining end of the thread to one of the lumbar vertebræ.
6. Put on each hind leg by drilling a small hole straight through the head of the femur and the socket of the pelvis (innominate bone), through which a small brass wire is to be passed and clinched down closely at each end, to hold the head of the femur firmly in place.
7. Place each leg in the attitude chosen for it, plant the foot according to its osteological character, and pin each toe in its proper place, as shown in the accompanying plate. The leg must be held in place by attaching threads to it, and making them fast to the various parts of the gallows.
8. In putting on the foreleg, the position of the scapula must be defined with accuracy, in order to avoid placing it too low or too high, and thus making an incorrect representation of the height of the animal. Bear in mind that the scapula never lies prone upon the ribs, but is separated from them by a cushion of muscle. It is therefore necessary to leave a certain space between ribs and scapula.
9. Next cut two stiff brass wires of the proper length for the two standards that must support the skeleton (see A A and B B in Plate XX.). To make the U-shaped fork at the upper end of each standard, to clasp the vertebral column, heat one end of the rod red-hot, and plunge it into cold water, which softens the metal. Now put it in a vise, and with a hack-saw split the rod down the middle as far from the end as necessary. Finish neatly by rounding off the ends with a fine file, and bending them in shape with the pliers. The lower end must have a thread cut on it an inch or so in length, a neat brass "rosette" screwed upon it (R) to do duty on the top of the pedestal, and a small brass nut made to screw on underneath the pedestal, to hold the standard firmly upright. These standards need not be put in place under the skeleton until it is mounted finally on its handsomely polished, permanent exhibition pedestal.
10. Mr. Lucas has two methods for attaching a small skull to the skeleton. One is to cut a piece of cork to fit snugly in the occipital hole of the skull (foramen magnum), then pierce a hole through its centre, and fit it tightly on the projecting end of the vertebral wire, close up to the first cervical vertebra (the axis). The cork thus becomes stationary, and the skull may be put in place and removed at will.
The other method is to place the skull exactly in position on the skeleton, fitting it closely to the axis. Then drill a small hole through each side of the axis in such a manner that in its passage from top to bottom the drill will also pass through the occipital condyle of the skull. By fitting a wire through each of these holes the skull will be held fast in position so long as the skeleton remains in its place, right side up. If the skeleton is to be packed for shipment, the skull (unless it be very small and light) must be taken off, wrapped, and packed separately for safety in transit.
[a]Fig. 69.]—Skeleton of a Bat, as exhibited by Mr. Lucas.
11. If any bones have been broken, they must now be repaired, either by gluing them together, or by joining with a short wire fitted into the axis of each piece, and the missing particles of bone may be restored by a filling of best sinew glue mixed with plaster Paris into a paste, and applied hot, so that it will adhere. As it cools it can be shaped properly, and when thoroughly dry and hard, its surface must be dressed down with a fine file and sand-paper until the form of the bone is once more perfect. This is work which very often calls for considerable skill in the operator, but the process itself is a very simple one.
If ligaments are missing and a small bone is completely detached, it should be put on as follows: Procure some fine cotton batting, cut it up very finely with the scissors, then apply some hot glue to the joint, lay a bit of clipped cotton upon it, and work it into the glue so that when dry it will form a false ligament and hold the bone firmly in its place without attracting any attention to the fact that the ligament has been made for the occasion.
12. Finally, transfer each skeleton to its permanent pedestal, which we will assume has been prepared while the specimen has been drying. Mr. Lucas puts all his small skeletons on handsome ebonized pedestals, which are the thing par excellence. The limbs for his climbing animals, and the thin, black boards for his bat skeletons are also ebonized. The illustration on page 291 (Fig. 69) shows one of his bat skeletons complete, as it stands in its case, bearing a label of black letters on an olive-gray card, with no ornamentation. In the final mounting the standards are put in place, and the upper end of each fitted fast to the backbone. Each toe is fixed firmly in its place, and held down by the bent-over end of a headless pin, or by having a pin put through it, and cut off close down to the bone.
[a]Fig. 70.]—Skeleton of a Bird Mounted and Drying.
Cautions and Exceptions.—It is only the tiny skeletons, such as mice, shrews, small squirrels, and the like, that can safely be mounted without standards. To be sure, a large cat skeleton can be mounted on its own legs, without any standards, and so can a man drink a pint of bad whiskey; but in each case the falling from grace will be in about the same degree, if not the same in kind also. In long-continued moist weather, ligaments are apt to soften and let large unsupported skeletons come down, without neatness, but plenty of despatch.
Birds.—The foregoing principles, which have been described in detail for small mammals, apply so fully and with such complete general similarity to birds, that it is only necessary to add the two accompanying illustrations.
[a]Fig. 71.]—Wiring a Skeleton Wing.
Reptiles.—Serpents.—The skeletons of serpents should always be scraped and mounted as ligamentary specimens, and not macerated. The skeleton should be supported on from three to five low brass standards clasping the vertebral column at proper intervals, the body curved naturally, and the ribs spread out and spaced evenly as in life, according to the curves of the body. The skeleton looks best when placed low down on the pedestal. The ribs must be spaced with threads where the ligaments are soft, but when dry require no wires. The skeleton may be mounted in any life-like attitude, either coiled or in motion.
Lizards.—Small species are to be treated the same as small mammals.
Crocodiles and Alligators.—It is best that all saurian skeletons, even the largest, should be scraped and mounted without maceration, on account of the elaborate cartilaginous sternum and false ribs. The head requires a special standard, and the tail requires a pair, while the tip of the latter is to be pinned down with a wire. Of course the feet must rest down on the pedestal as in life. One thing which would greatly enhance the scientific value of every crocodile and alligator skeleton would be the preparation and display, in its proper place, of one side of the skin of the back with its wonderful shield of bony plates nicely articulated together. This remarkable covering of the vital organs seems to have been specially designed to ward off glancing bullets, and it has saved the lives of thousands of crocodilians. (Of course this shield is not proof against a bullet fired squarely against it.) So far, all collectors and osteologists have ignored this remarkable feature of the saurians, but it should have the attention it deserves.
[a]Fig. 72.]—Skeleton of Turtle, as Exhibited.
Turtles and Tortoises.—The skeleton of a tortoise, if mounted on its feet in a life-like attitude, has the best part of its anatomy concealed by its shell. This difficulty Mr. Lucas meets occasionally by sawing out and laying back one-half the carapace, to expose the interior. The commonest method, however, is that shown in the accompanying illustration (Fig. 72), which is self-explanatory. The plastron is hinged at one side, furnished with a latch, and opens like a door. The skeleton is mounted on a single standard, which is split at the upper end like a Y, the arms bent to fit the curvature of the shell, and riveted to the carapace. Each leg is held in place by a small wire attached to the shell at its edge.
Fishes.—There is nothing in the mounting of fish skeletons that has not been fully described in the foregoing pages. Of course fish skeletons are never macerated, but must be scraped and mounted with their natural ligaments in place. Each skeleton requires two brass standards, one clasping the vertebral column close to the tail, the other near the head. A very long fish, or one with a large skull, requires three standards, one for the skull and one for the middle of the body. Where only two are used for a large fish, the head requires to be supported by a wire running from the centre of the backbone.
[CHAPTER XXXIX.]
MOUNTING A LARGE DISARTICULATED SKELETON.
It will be well for anyone who intends to mount a large skeleton, if he has not already a fair knowledge of osteology, to take some book which contains a description of the skeleton, for example, of the domestic cow, and familiarize himself with the names of the various bones and the different anatomical terms used in describing them. In fact it is next to impossible to describe the process of mounting a skeleton without making use of quite an array of technical terms.
In order to make our description of this intricate process as clear as possible, we will choose as our typical subject the skeleton of an American bison, and go through with it in detail, aided by an abundant supply of illustrations. We of course assume that the macerating, cleaning, and bleaching has been done.
In mounting a disarticulated skeleton, begin with the vertebral column as the key to the situation. It is, in point of fact, the keel upon which the whole structure is to be built. The vertebræ should be arranged, each in its place, and, then they should be numbered with pen and ink on the anterior articulating surface of the body of each one, beginning with the first vertebra in front of the sacrum. This vertebra (the last lumbar) should be marked No. 1, the next in front No. 2, and so on to the axis.
The next step consists in boring two holes through the sacrum from its under surface (Fig. 73, a, a) to its anterior articulating surface (b, b), and these holes should be continued on through the body of each of the succeeding vertebrae to the axis. They should come out underneath that vertebra (the axis), where the wires which pass through all these holes are afterward to be twisted together. The holes should be somewhat larger than the brass wires which are to pass through them.
It is necessary to mark the place for starting the drill into the posterior surface of each vertebra by fitting two articulating surfaces together, and passing the drill through the holes already made. The points at which the drill should come out on the anterior surface of a vertebra should be marked with a lead pencil. The beginner will find some difficulty in making the drill come through at precisely the right spot. The greatest difficulty will be experienced in getting these holes through the cervical vertebrae.
When the axis is reached, bore the holes so that they will come out underneath, about half way between each extremity of the vertebra, and about three-fourths of an inch apart.
It is just as well to now bore the holes through which the wires which fasten the axis and atlas together are to pass, though these need not be actually united until the remainder of the spinal column has been, articulated. The wires uniting the atlas and axis are smaller than those passing through the spinal column. The holes for these wires are made by boring two of them through each of the two surfaces by which the axis articulates with the atlas. These holes should come out underneath the axis. Then, placing the axis and atlas together, mark on the atlas the places through which the holes are to pass by running the drill through each of the holes already made.
The next thing to be done is to cut pieces of artificial cartilage, called "buffle," to fit the posterior articulating surface of the body of each vertebra, and each piece should be fastened to the vertebra to which it belongs by a small wire nail through its centre. The holes in each vertebra should be continued straight on through the false cartilage. Now cut a brass wire three times the length of the spinal column, double it, pull it straight, pass the two ends through the sacrum, and so on forward through all the vertebræ.
When the vertebræ have all been strung on the two wires and tightened up, it will be seen that the spinal column assumes a curve approximating very nearly to the natural one. Mark this curve with chalk on a table or a board.
Unstring the vertebræ from the wire. Then take a square rod of iron, a foot or so longer than the spinal column, and over which each of the vertebra will fit easily. Have the blacksmith flatten out one end into a sort of spear, so that it will fit snugly in the spinal canal of the sacrum (Fig. 73, c).
[a]Fig. 73.]—The Sacrum and Spinal Rod.
Drill a hole through the under surface of the sacrum, and on through the iron rod: Into this a brass pin is to be fitted at d. Bend the iron rod to correspond exactly with the curve previously marked with chalk on the board. Paint the rod black, and when it has dried place it again in the sacrum, drive in the brass pin, leaving enough of the end exposed to be seized with a pair of pliers and pulled out if desired. Now string the vertebræ over the rod and wires. If all fit properly they can then be unstrung preparatory to attaching the ribs to them.
[a]Fig. 74.]—The Attachment of the Ribs to a Vertebra.
Each rib should have a hole bored through its lower end at the middle, to come out on the inner surface (Fig. 74, b, b). Through these holes wires are to pass, as seen in the accompanying figure, and to these wires the sternum is presently to be attached.
Having arranged the ribs so that you know the place of each, take the first pair, and the first dorsal vertebra to which this pair attaches. Bore a hole with the drilling machine through the rib, beginning at the centre of the articular surface of the tubercle of the rib, directing the drill so that it will come out on the under side (Fig. 74, c, c); then drill a hole through the head of the rib (d, d). Now fit the rib to the vertebra, and with a small awl, a sharp-pointed wire, or drill, mark, through the holes already made, the points on the articular surface of the vertebra through which the holes should be drilled (a, a). Bore similar holes through the rib of the opposite side, then through the vertebra at the points marked, and the wire will pass through as in the figure.
PLATE XXI.
[a]Skeleton of an American Bison.]
Continue this same process for the remaining ribs. It will be found, however, that the process of carrying a single wire through the heads of both ribs and the anterior portion of the body of the vertebra cannot be continued with all. In the last of the dorsal vertebrae the wires will have to be put through the head of the rib and the pedicles of the vertebrae into the neural canal.
Make a loop on the end of each wire, as at a, a, Fig. 74, and put the ribs on each vertebra as they belong, having only one end of the wire—the one on which is made a double loop—pulled up snugly. The other end of the wire should be left a few inches in length, but bent slightly close to the rib, to hold the latter in place.
The innominate bones should be attached to the sacrum either by two brass bolts, one passing through each side at about the middle of the articular surfaces between the sacrum and each ilium, or by passing a heavy double wire through each of these places. Before tightening permanently, apply "plaster-glue" (the mixture of glue and plaster Paris already described) to the articular surfaces between the sacrum and ilia, thus when dry making the pelvis firm.
Now that the ribs are attached to the vertebræ, and the innominate bones to the sacrum, proceed to string the vertebræ again on the wires and rod. The atlas can now be attached to the axis by passing wires through the holes previously made, after which the wires are to be twisted firmly together.
When all the vertebræ with their ribs attached have been put in place, hang the backbone to a framework similar to that used for suspending the alligator (Plate XIV.), or, what is much better, to the ceiling, by two small ropes attached at the neck and pelvis.
With the pliers now twist tightly together the wires under the axis, then take a screw-driver and work between each pair of vertebrae from underneath, beginning with the last lumbar, and prying back toward the sacrum. By the time you have reached the axis a considerable space will have been gained. Shorten the wires by twisting them, and continue this process until the vertebrae all fit snugly together, and are tight one against the other.
[a]Fig. 76.]—Middle Joint of the Hind Leg.
The next step is to put on the sternum, which has been soaked in water containing a little washing soda, and thus made flexible. Of course it has been previously cleaned by the scraping process. A hole should be bored through the end of each sternal rib, coming out on the inner surface. The sternum is suspended temporarily by strings attached to the vertebral column, and the single wires that have previously been placed through the end of each rib are now run, one by one, through the end of the sternal rib it is to support.
Now space the ribs temporarily with a string that will hold each one of them exactly in its place. Having done this, two brass wires can now be used to hold the ribs permanently in place, running them on each side from the inferior process of the last cervical vertebræ to the transverse process of some one of the lumbar vertebra, or to the pelvis. What is much better for a large skeleton, because it is both firmer and more elegant, is a long, narrow strip of polished brass on the inside, bent carefully to fit the curve of the ribs, and fastened by a brass pin through each rib, the posterior end of the brass strip being attached to a transverse process of one of the lumbar vertebræ (see Plate XXI.). After this has been done, each rib can then be permanently fastened at top and bottom by making the loop and cutting off the long end of each wire.
[a]Fig. 76.]—Middle Joint of Hind Leg: Rear View.
The next step is to put on the tail. A hole should have been bored into the middle of the articular surface of the posterior end of the sacrum, and on each side a little hole coming out below (see Fig. 73). The large middle wire (e, e) should be of stiff brass, and extend through the entire length of the tail, the tapering end being filed small so that the small vertebræ can fit over it. The small side wires of soft brass (f, f) should only extend through a few of the larger tail vertebræ, and are for making things firm.
[a]Fig. 77.]—Bones of the Foot: Side View.
To articulate the bones of the hind leg, first arrange them so as to know the precise place of each. Take first the tarsal and metatarsal bones. In articulating these it is necessary for one to use his judgment largely, and put wires through so as to make the joint firm. Bore holes through the astragalus and os calcis (Fig. 75, a, a) so as to put a double wire through these and hold them together firmly. Next send two strong double wires through these and through the other tarsal bones, and bring them out on the posterior surface of the metatarsal or canon bone (c and d).
[a]Fig. 78.]—Bones of the Foot: Rear View.
Next articulate the bones of the feet. This is very simply done by passing a single heavy wire through the lower end of each half of the canon bone to each set of phalanges, making a loop at each end of the wire (see Figs. 77 and 78). In large skeletons it will frequently be found necessary to further strengthen the articulations of the phalanges by means of brass pins, as shown in the figure at a. The sesamoids are fastened on by two stiff brass pins through each at b.
The femur and tibia can be fastened together by a double brass wire passing through each condyle of the femur, and through each side of the head of the tibia, or, what is better, a strip of brass set into the middle of the joint, and fastened firmly by two stout brass pins driven transversely through from side to side, as indicated in Fig. 79.
[a]Fig. 79.]—The Knee-Joint.
The patella is fastened on by passing a wire through it and twisting it, or erecting it on a small strip of brass set into the tubercle of the tibia. The joint is further strengthened by putting a brass pin through the patella into the end of the femur.
The tibia is articulated to the lower portion of the leg, or, more properly, the pes, by putting stiff wire pins into it. The femur is articulated to the pelvis by a brass bolt. The front foot is articulated on the same principles as the hind foot.
[a]Fig. 80.]—Front View of Knee-Joint.
In articulating the knee-joint, as it is called, send two heavy wires through, letting them come out on the posterior surface of the radius and metacarpal bone, and insert two wire pins diagonally through the joint, as shown in Fig. 81. The scapula is fastened to the humerus by brass pins. The humerus, radius, and ulna are also fastened by brass pins, three in number.
[a]Fig. 81.]—Elbow Joint: Front View.
The scapula is attached to the body by two brass bolts attached to the ribs. Sections of spiral spring wire or pieces of brass tube are placed on the bolts between the scapula and the ribs, to hold the former off the latter the same distance as when the flesh surrounding the scapula was all present. As to the position of the legs, the operator must use his own judgment. It is of course to be understood that the attitude of the legs has been decided upon before their articulation began, and that the work of wiring together has been carried out in accordance with this plan. It is hard to do more with a large skeleton than to place the legs in an easy walking attitude, of which the buffalo skeleton already figured may fairly be taken as a model.
The rod extending through the spinal canal is cut off so that the head will hang on it properly. Two brass pins are passed through the atlas, one into each occipital condyle. Two iron rods, with lacquered brass shoulders, are used to support the skeleton, as shown in the figure. These rods should be painted black.
The lower jaw is fastened to the skull by means of brass spiral spring wire, which permits it to be moved freely up and down by any one who is studying the animal's dentition.
The method of mounting any large disarticulated skeleton of a quadruped is essentially the same as that described for the buffalo, the principle variation occurring in the feet. In articulating the feet of a wolf, for example, the method of wiring the tarsal bones, carpal bones, metatarsals, metacarpals, and the phalanges, is very similar to that described for the buffalo, but the workman must here also depend largely on his own ingenuity. A single wire passes through the phalanges of each digit, and two sesamoids are fastened on by a single wire.
Where the digits are more than two in number, a wire is passed transversely through the lower ends of the metacarpals and metatarsals, and on this are placed short pieces of fine coiled brass spring, to hold the digits at proper distances from one another.
The tools used in mounting large skeletons are by no means so numerous or costly that any one need be deterred from trying his hand at practical osteology on the score of facilities or the lack of them. Of course the complete outfit of a professional osteologist includes an extensive array of tools, some of which are rather costly. The most important item is a good drilling machine, chuck and lathe, to work by foot-power. This can be procured of Goodnow & Wightman, of Boston, and in ordering it will be necessary to have a 1/4-inch hole drilled through the centre of the axle, to receive the long, steel drills of various sizes that are to drill the many holes required in the various bones.
The amateur who can not afford an expensive plant and a first-class drilling machine, can get along very well with a Millers' Falls hand-drill and a good assortment of first-class steel drills to fit it. I once saw an old German anatomist mount a cow skeleton for a Western college with hardly more tools than I could hold in one hand—but, of course, that skeleton was not mounted à la Lucas, by a considerable difference.