The Nasal Bones
| The nasal bones of the dog, as seen opposite, are very small, as they are in all carnivorous animals. Instead of
constituting the roof, and part of the outer wall of the cavity, as in
other animals, the nasal bones form only a portion, and a small one, of
the roof. [N. B. This image does not enlarge well, but a magnifying glass may serve. html Ed.] |
The
superior maxillaries
here swell into importance, and constitute the whole of the outer wall, and, sometimes, a part of the roof. The jaws are the weapons of offence and defence; and as much space as possible is devoted to the insertion of those muscles that will enable the animal to seize and to hold his prey. One of the most powerful of them, the
masseter
, rises from the superior maxillary bone, and spreads over its whole extent: therefore, that bone is developed, while the nasal bone is compressed into a very small space. The substitution of a portion of cartilage, instead of bone, at the posterior part of the orbital ring, in order to give more play for the coracoid process of the posterior maxillary, round which the temporal bone is wrapped, is a contrivance of the same nature.
The scent of the dog is not sacrificed or impaired by the apparent diminution of the nasals; for the cavity enlarges considerably upward, and is occupied chiefly by the
ethmoid bone
, which, having the greater portion of nervous pulp spread on it, seems to have most to do with the sense of smell.
The nasal bones of the dog are essentially different from those of the horse, cattle, and sheep. They commence, indeed, as high up in the face as those of the horse, their superior extremities being opposite to the lachrymal gland; but that commencement is an apex or point varying materially in different breeds. They form, altogether, one sharp projection, and are received within breeds these processes extend nearly one-third of the length of the nasals.
The superior maxillary (3.3.) takes the situation of the nasal (2.), pushes the lachrymal bone (4.) out of its place, and almost annihilates it, reaches the frontal bone (7.) and expands upon it, and forms with it the same denticulated suture which is to be seen in the nasal. The action of the muscle between these bones, and for the development of which all this sacrifice is made, is exceedingly powerful. The strength of this muscle in a large dog is almost incredible: the sutures between these bones must possess corresponding strength; and so strong is the union between them, that, in many old dogs, the suture between the superior maxillary and frontal bones is nearly obliterated, and that between the nasal and frontal maxillary quite effaced.
As the nasal bones proceed downward they become somewhat wider. They unite with a long process of the anterior maxillary for the purpose of strength, and then terminate in a singular way. They have their apexes or points on the outer edge of the bone; and these apexes or points are so contrived, that, lying upon, and seemingly losing themselves, on the processes of the anterior maxillary, they complete, superiorly and posteriorly, that elliptical bony opening into the nose which was commenced by the maxillary anteriorly and inferiorly. The nasal cavity of the dog, therefore, and of all carnivorous animals, terminates by a somewhat circular opening, more or less in the form of an ellipse. This bony aperture varies in size in different dogs, and, as we should expect from what we have seen of the adaptation of structure to the situation and wants of the animal, it is largest in those on whom we are most dependent for speed and stoutness.
olfactory
, or first pair of nerves, have a double origin, namely, from the
corpus striatum
and the base of the
corpus callosum
. They are prolongations of the medullary substance of the central portion of the brain. They are the largest of the cerebral nerves. Their course is exceedingly short; and they have not a single anastomosis, in order that the impression made on them may be conveyed undisturbed and perfect to the brain.
The olfactory nerve is a prolongation of the substance of the brain, and it abuts upon the cribriform bone, of which mention has been made. I will not speak of the singular cavities which it contains, nor of their function; this belongs to the sensorial system: but its pulpy matter has already been traced to the base of the ethmoid bone, and the under part of the septum, and the superior turbinated bone. Although we soon lose it in the mucous membrane of the nose, there is little doubt that in a more filmy form it is spread over the whole of the cavity, and probably over all the sinuses of the face and head. It is, however, so mingled with the mucous membrane, that no power of the lens has enabled us to follow it so far. It is like the
portio mollis
of the seventh pair, eluding the eye, but existing in sufficient substances for the performance of its important functions.
We have frequent cases of
ozæna
in old dogs, and sometimes in those that are younger. The discharge from the nostril is abundant and constant, and sometimes fetid. The Schneiderian membrane, of more than usual sensibility in this animal, is exposed to many causes of irritation, and debilitated and worn out before its time. Pugs are particularly subject to ozæna. I scarcely ever knew a very old pug that had it not to a greater or less degree. The peculiar depression between the nasal and frontal bones in this breed of dogs, while it almost totally obliterates the frontal sinuses, may narrow the air-passage at that spot, and cause greater irritation there from the unusual rush of the air, and especially if the membrane becomes inflamed or any foreign body insinuates itself.
Little can be done in these cases, except to encourage cleanliness about the face and nostrils. It is, in the majority of these cases, a disease of old age, and must take its course.
A terrier uttered a continual loud stertorous sound in breathing, which could be plainly heard in our parlour when the dog was in the hospital. The animal was evidently much oppressed and in considerable pain. He made continual, and generally ineffectual, efforts to sneeze. When he did succeed, a very small quantity of pus-like fluid was discharged; the dog was then considerably relieved, but a quarter of an hour afterwards he was as bad as ever. I ordered a slight emetic every third day. There was some relief for seven or eight hours, and then he was as bad as ever. I could neither feel nor see any cause of obstruction. The owner became tired, and the dog was taken away; but we could not learn what became of it.
Another terrier was occasionally brought for consultation. The dog breathed with considerable difficulty, and occasionally snorted with the greatest violence, and bloody purulent matter was discharged; after which he was somewhat relieved; but, in the course of a few days, the obstruction was as great as ever. I am not aware of a single instances of this affection of the pug being completely removed. The discharge from the nostrils of the bull-dog is often considerable, and, once being thoroughly established, is almost as obstinate as in the pug.
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