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In early childhood, the bones of the head are separate to allow the brain to expand; but as we grow older they gradually unite, the better to protect the delicate brain tissue. The Cranium. The cranium is a dome-like structure, made up in the adult of 8 distinct bones firmly locked together. These bones are: One Frontal, Two Parietal, Two Temporal One Occipital, One Sphenoid, One Ethmoid.
It could be only the sternest of research and experience which dictated such sentences as these: The especial dangers to be contended with are that the ethmoid cells may be mistaken for the sphenoids; that we may go too low and enter the pons and medulla; that, laterally, we may enter the cavernous sinus, and above, that we may injure the optic nerve.
The cranial nerves are of three kinds: sensory, motor, and both combined, viz., mixed. Distribution and Functions of the Cranial Nerves. The cranial nerves are thus arranged in pairs: The first pair are the olfactory nerves, which pass down through the ethmoid bone into the nasal cavities, and are spread over the inner surface of the nose. They are sensory, and are the special nerves of smell.
A part of the right malar bone, the two superior maxillary bones, the nasal bones, the cartilage, the vomer, the middle lamina of the ethmoid, the left maxillary bone, a portion of the left zygomatic arch, and a great portion of the inferior maxilla were carried away, or comminuted, and all the soft parts correspondingly lacerated.
If to this is added, that the olfactory or first pair of nerves abut on these cribriform plates, and pass through their minute openings, and spread themselves over every one of these cells, we have a tolerably correct picture of this portion of the ethmoid bones. This nerve has different degrees of development in different animals, in proportion to their acuteness of smell.
It is also much more fragile in the dog than in the ox, and the plates have a considerably thinner structure. The ethmoid bone of the horse or the ox may be removed from its situation with little injury; but that of the dog can scarcely be meddled with without fracture. Below it are the two turbinated bones; but they are reduced to insignificance by the bulk of the ethmoid bone.
While it is white and without smell, and the dog is not too much emaciated, the termination may be favourable; but when it becomes of a darker colour, and mingled with blood, and offensive, the ethmoid or turbinated bones are becoming carious, and death supervenes.
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.
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.
The inflammation at the same time seizes on the membranes of the nostrils, and those lining the bones of the nose, particularly the nasal portion of the ethmoid bone. These membranes are often inflamed to such a degree as to occasion extravasation of blood, which I have observed coagulated on their surface.
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