152 COMPARATIVE ANATOMY AND PATHOLOGY. 
the ramifications of the nerve shall be conveyed undisturbed and 
perfect to the brain. 
The Ethmoid Bone . — When speaking of the respiratory system, 
seven years ago, in the second number of the fifth volume of The 
Veterinarian, the structure of that portion of the ethmoid bone 
on which the olfactory nerve abuts was sufficiently described. It 
is a thin perforated plate of bone, called on this account the cribri- 
form or sieve-like lamella. It occupies the chasm between the 
base of the ethmoid bone and the frontals. On this the olfactory 
nerve abuts, and through its minute foramina the pulpy matter 
of this nerve passes. From the bony arch which surrounds this 
plate arises a pear-shaped collection of thin, porous, bony cells. 
They may be likened to a great number of little hollow pedicles 
proceeding from and forming around the cribriform plate. As they 
move downward, they belly out into distinct vesicles or cavities ; 
smaller and more numerous behind, fewer in number and larger in 
front, and each of them, not a simple cavity, but more or less con- 
voluted, while the bony walls of each is of gossamer thinness, and 
porous as any gauze. All of them communicate together, and are 
lined inside and out by the Schneiderian membrane — the whole 
assuming a pear-like shape, attached by its base or greater extre- 
mity — decreasing in size as it proceeds downwards — the cells be- 
coming fewer, and terminating at length in one cell — a kind of 
pedicle or stalk, which passes under the superior turbinated bone, 
and communicates with the central meatus, and forms a kind of 
valve over the opening between the nasal cavity and the maxillary 
sinuses. I am nearly repeating the account which I gave of it 
when speaking of the respiratory passages in the horse. All of my 
present readers may not be in possession of the early volumes of 
The Veterinarian. 
On these curiously constructed bones the olfactory nerve, hav- 
ing threaded the cribriform plate, ramifies. It passes through their 
minute openings, and spreads itself over every one of these little 
cells. On a portion of these cells the pulpy fibres may be seen 
to ramify, and they are, doubtless, diffused over every part. 
The Ethmoid Bone in different Animals . — The ox is not so 
domesticated an animal as the horse. He has more occasion for 
acuteness of smell, and particularly in the early part of the 
spring, when the plants are young, and have not acquired their full 
scent ; therefore the ethmoid bone is much larger in him than in 
the horse. It is comparatively larger in the sheep than in the ox, 
on account of the greater approach to liberty which this animal 
enjoys. In the omnivorous swine it is yet more developed ; for 
he often has to search for a portion of his food deep in the mire, or 
deeper still under the surface of the ground. In the cat, and the 
