THE VISCERA.

Kill the specimen with chloroform and inject with the five per cent. formalin, or the mixture of formalin and glycerine, as for the muscles. (It is an advantage if the preliminary examination of the viscera can be done in a perfectly fresh, uninjected specimen; such a specimen can be kept but a day or two, however. After one day’s examination the skin may be removed and the specimen placed in two per cent. formalin; it will usually be fairly well preserved by this, though the formalin is too strong to make the later dissection pleasant. The specimen cannot be preserved in this manner unless the skin is removed, and a sufficient quantity of formalin used.)

Preliminary Examination of the Viscera.

(In this preliminary examination the descriptions in the text need not be read, except when this is specially directed.)

Wet the hair along a line from the symphysis of the jaw to the pubis. Part it and make a longitudinal incision through the skin along the line. Make a transverse incision of the skin five centimeters caudad of the xiphoid process and reflect the flaps. Incise the body wall from the last rib to the pelvis along the same line as above and also transversely. Reflect the flaps without injuring the ligaments of the bladder. Make an incision through the pectoral muscles between the first rib and the ventral attachment of the diaphragm and about one centimeter from the median line. Make a second incision of the muscles from the cranial end of the first incision along the angles of the ribs to near the dorsolateral attachment of the diaphragm. Cut the ribs and thoracic wall along these incisions with strong scissors; connect the two incisions at their caudal ends, and remove the lateral thoracic wall thus circumscribed. Note the thoracic and abdominal cavities, separated by the diaphragm.

Note the following viscera in their fresh condition:

A. In the abdominal cavity (without injuring anything)

1. The liver, dark red and lobed, in the cranial part of the cavity, lying against the diaphragm.

2. The gall-bladder partly imbedded in the right median lobe.

3. Displacing the liver craniad, the stomach is seen dorsad of its left lobe. It may extend dorsad of the right lobe, its size depending on the degree of distension.

4. The duodenum or first part of the small intestine leaves the stomach at its right side craniad and makes a U bend, the head of which is directed caudad; it then turns toward the middle line dorsad of the remaining part of the small intestine.

5. The great omentum is a thin fold of peritoneum with many bands of fat. It passes like a curtain from the great curvature of the stomach ventrad of the coils of the small intestine (ileum). It is tucked beneath the mass of coils at the sides and caudally, and folds of it extend between the individual coils. Turn it craniad and note—

6. The numerous coils of the third part of the small intestine or ileum. Turn these to one side and note—

7. The connection of the ileum with the duodenum across the middle line. An indefinite part of the intestine between the ileum and duodenum is called the jejunum, because in man it is found empty after death.

8. The passage of the ileum into the side of the large intestine which begins on the right side just caudad of the loops of the duodenum. The first part of the large intestine is the colon. It may be traced first toward the head (ascending colon), then sinistro-caudad (transverse colon) and then caudad (descending colon). The descending colon returns to the middle line and the large intestine then continues to the anus as the rectum.

The blind pouch of the colon which lies caudad of the opening of the ileum is the cæcum.

9. Turn the duodenum toward the left and note the pancreas, a light red, elongated organ which stretches along the greater curvature of the stomach and thence between the two lines of the duodenal U to its bottom.

10. The spleen, parallel to the gastric portion of the pancreas. It is deep red (darker than the pancreas and not so brown as the liver) and is held against the great curvature of the stomach by a part of the great omentum.

11. The kidneys, close against the dorsal body wall and in contact with the caudal part of the liver.

12. The bladder, in the median line at the caudal end of the cavity, held in place by the suspensory ligament, which passes to the midventral line, and by the lateral ligaments.

13. The mesenteric glands, large grayish-red glands one to four centimeters long, more numerous in the mesocolon.

14. In the female, lying against the ventral surface of the rectum, the uterus. It divides into two horns which diverge. Near the end of each horn the ovary.

15. The peritoneum. Study and understand the description of it ([p. 218]). Dissect some of it free from the body wall. (Trace the folds by aid of a diagram and model.)

B. In the thoracic cavity:

1. The lungs. Each is divided into lobes, three on the left, four on the right. The caudal right lobe pushes the mediastium toward the left and thus lies in a pocket dorsocaudad of the heart and dorsad of the vena cava inferior.

2. The pleuræ. Each pleura is a membrane like the peritoneum. It covers the diaphragm and the thoracic walls and is reflected onto the lungs. Hence it is divided into costal and pulmonary portions. Read the description ([p. 217]) and trace their connection. Each pleura forms a closed sac.

3. The mediastinal septum or median vertical portion formed by the apposition of the medial walls of the two pleural sacs. It divides the thorax into halves.

4. In the mediastinum or space between the halves of the mediastinal septum are seen—

a. Ventrally (i.e., in the anterior mediastinum), blood-vessels and fat, and craniad the pink thymus gland. Read the description of the thymus ([p. 254], and [Fig. 107]).

b. Dorsally (i.e., in the posterior mediastinum) the trachea (best seen craniad), the œsophagus (best seen caudad), and the aorta.

c. In the middle (reckoning in a dorsoventral line) (i.e., in the middle mediastinum) the heart, with the inferior vena cava approaching it from the rear. Prick into the mediastinum and inflate it. Remove the thoracic wall opposite the one already removed, so as to stretch the mediastinum and show it more clearly. Expose the trachea beneath the caudal end of the sternomastoidei. Note the thyroid gland ([Fig. 96], 6, [p. 229]). Insert a blowpipe without injury to the thyroid, and inflate the lungs. Cut the sternum at its caudal end and turn it craniad, cutting the mediastinal septum and noting its double character.

Dissect the mediastinal septum from the thymus so as to expose this organ.

d. The pericardium, a relatively thick-walled sac, within which the heart lies. The pericardium is covered by the mediastinal septum on each side, but not dorsally and ventrally. Dissect the mediastinal septum from the pericardium. Prick and inflate the pericardium. Open it and expose the heart.

Dissection of the Alimentary Canal.

Study and verify the descriptions of the organs as they are dissected.

I. Salivary glands ([p. 223]).

1. Keep the mouth open by a cork between the teeth. Find the papillæ upon which open the sublingual and submaxillary ducts (p[p. 223] and 224); remove the mucosa and enlarge the opening and insert a black bristle into either duct. Trace the duct by the bristle as far as possible on the floor of the mouth.

2. Find the white ridge formed on the cheek by the parotid duct ([p. 223]). It is opposite the molar tooth, and at its cranial end the opening of the duct is seen. Enlarge the opening and insert a black bristle as far as possible.

3. Remove the skin and the skin-muscles from the side of the face, beginning at the caudal end and working craniad. At the cranial border of the carotid on the ventral side look carefully for the parotid duct with the bristle in it. The duct is then easily traced by the removal of the skin and muscles. Study the parotid gland ([Fig. 131], 10, [p. 322]).

4. Remove the facial vein ([Fig. 131], b and c) and lymphatic gland ([Fig. 131], 12) covering the submaxillary gland ([Fig. 131], 11) and clean its outer surface. Raise it and find the submaxillary duct leaving its inner surface. Reflect the digastric and mylohyoid muscles and trace the duct to the oral mucosa. The remainder of its course is shown by the bristle on the inside of the mouth.

5. The sublingual gland is uncovered in dissecting the submaxillary. Its duct is seen by the side of the submaxillary. It may be pricked near the gland and a bristle passed to its opening.

6. The infraorbital gland. Expose it by removal of the zygomatic arch and masseter muscle. Find its duct by dissecting apart the lobules at its ventral end. Prick the duct and insert a bristle to find its inner opening.

7. The molar gland. Find it by raising the orbicularis oris of the lower lip. By raising its ventral border and dissecting between it and the mucosa the ducts may be found and perhaps pricked and bristles inserted.

II. The mouth-cavity. Study the general description ([p. 221]); the lips and the cheek. Then remove the masseter muscle and the caudal part of the zygoma. Cut through the mandible between the first premolar and the canine tooth. Then disarticulate the mandible, cut the cheek and also the mylohyoid muscle and oral mucosa parallel to the medial border of the mandible, and remove the mandible with the parts thus left attached to it. The organs in the mouth-cavity are thus left exposed and should be studied. To demonstrate the incisive ducts ([p. 222]) pass a bristle into them.

The teeth ([p. 224]). These should be studied on a skull in which the roots of the teeth have been laid bare by means of the bone-forceps, as in [Figs. 93] and [94].

The tongue ([p. 226], and [Fig. 95]). Study its dorsal surface, the papillæ, etc. Then dissect its muscles ([p. 228]) from the ventral side. The stylohyoid, digastric, and mylohyoid muscles must be removed. Then dissect (a) the styloglossus ([Fig. 96], e), (b) the genioglossus ([Fig. 96], f), (c) the hyoglossus ([Fig. 96], h). Make a transverse section of the tongue to see the intrinsic muscle-fibres.

III. The thyroid gland ([p. 254], and [Fig. 96], 6). Clean the sternomastoid muscles. Cut their interdigitating portions along the median line and reflect them. Find the lateral lobe of the thyroid gland beneath the lateral borders of the sternohyoid muscles. Dissect it, being careful not to destroy the delicate isthmus.

IV. The pharynx ([p. 231]). Remove the large lymphatic gland between the atlantal transverse process and the larynx. Clean the outer surface of the pharynx. Dissect the muscles of the pharynx ([p. 232]) as follows:

(a) The inferior constrictor ([Fig. 96], k).

(b) The middle constrictor ([Fig. 96], j).

(d) The stylopharyngeus ([Fig. 96], l).

The superior constrictor cannot well be seen at this point; it will be examined later.

Disarticulate the cranial cornu of the hyoid from the bulla tympani and make an incision the length of the lateral wall of the pharynx so as to expose its cavity; study. Examine its opening into the mouth-cavity and study the general description ([p. 231]). Find and study the soft palate ([p. 230]). Dissect the tensor and levator palatini muscles ([p. 230], and [Fig. 66], d and e, [p. 112]), using, if necessary, the specimen on which the other muscles were dissected. Then slit the soft palate lengthwise at one side of the median line to expose the nasopharynx ([p. 231]). Bring the choanæ into view by use of a bit of mirror-glass. Pass a bristle into the nares and out at the choanæ. Pass a bristle through the Eustachian tube into the middle ear.

V. Œsophagus ([p. 234]). After completing the study of the pharynx, leave the larynx and lungs in position and by displacing them toward the right follow the œsophagus to its termination. Open it to see the folds of the mucosa.

VI. Cut through the duodenum at its distal end and through the duodenal mesentery so as to separate the stomach and duodenum, with the liver, pancreas, and spleen, from the remainder of the alimentary canal. Float the parts in a dish of water.

VII. Study the stomach ([p. 234], and [Fig. 97]). Cut out the ventral wall of the stomach and wash it out, so as to study its cavity, and then continue the cut so as to expose the pyloric valve ([p. 235]).

VIII. Study the duodenum ([p. 236]). Cut away the ventral walls of the duodenum far enough to expose the ampulla of Vater.

IX. Study the liver ([p. 239], and [Figs. 100] and [101]). Expose the hepatic duct of the left lateral lobe near its entrance into the lobe, and follow it so as to expose it fully. If necessary, prick it and inflate with blowpipe in order to follow it. Then expose the cystic duct and other hepatic ducts and follow them to or from the common bile-duct. Trace the latter to the duodenum. If the air does not enter any duct readily, it may be made to do so by manipulating the duct so as to break up the precipitated bile which obstructs it.

X. Study the pancreas ([p. 241], and [Fig. 102]). Expose the pancreatic duct near its entrance into the ampulla of Vater, by removing the peritoneum from the pancreas just caudad of the end of the common bile-duct, and by dissecting apart the pancreatic lobules until the duct appears. (If possible, expose also the accessory duct in the same way on the ventral side of the pancreas, two centimeters caudoventrad of the ampulla of Vater. Prick and inflate. Trace its connection with the main duct. To demonstrate its opening pass a bristle through an opening in it into the duodenum.) (The pancreatic duct may be injected, if desired.)

XI. The ventral wall of the duodenum should now be removed. Cut out a small piece, clean its mucosa with a fine brush and examine the villi with a lens. Demonstrate the coats of the duodenal wall by stripping them off with forceps.

XII. The ampulla of Vater ([p. 236]). Pass bristles through openings in the common bile-duct and pancreatic duct into the duodenum through the ampulla. Slice away the duodenal wall parallel to the bristles until the bristles are exposed.

XIII. The spleen ([p. 242], and [Fig. 102]).

XIV. Cut the mesentery from the small intestine and colon and slit them both lengthwise, but do not destroy the ileocolic valve. Wash and brush the mucous membrane clean and study the villi, solitary glands, and Peyer’s patches. Study the ileocolic valve ([Fig. 99]) and open it to study its inner surface.