502 COMPARATIVE ANATOMY AND PATHOLOGY. 
the manner in which their important functions are discharged, and 
the diseases to which they are subject. 
The Orbit of the Eye. — -We shall perhaps most advantage- 
ously pursue our subject by considering the situation and external 
protection of the eye. We find it lodged in a bony orbit or socket ; 
somewhat differently placed, and differently formed in different 
animals. In the human being and in the quadrumana the defence 
of the eye superiorly, inferiorly, posteriorly, and laterally, is com- 
posed of bone. The comparatively little extent of motion which 
the posterior maxillary bone requires in the act of mastication in 
these animals permits of the outer sides of the orbit being con- 
structed of bony matter ; and by means of which somewhat greater 
security is given both to the bones of the cranium and the orbit, 
and more room is left for the development of the lateral portions of 
the brain. 
Difference in different Animals. — The orbit in our quadruped 
patients is different from that of the bimana or the quadrumana. 
It is an imperfect socket. In all of them it is so posteriorly, and 
in some of them anteriorly. In the horse and in the ruminant “ the 
supero-anterior part, about two-fifths of the external circumference, 
is formed by the orbital process of the frontal bone — the infero-an- 
terior part by the lachrymal bone, and the remainder by the malar 
and temporal bones.” The whole of the external ridge is bony. 
In the hog and all omnivorous animals, and in the cat and all car- 
nivorous ones, cartilage is substituted for the orbital process of the 
frontal bone. 
“ Internally the floor is constituted of the orbital plates of the 
lachrymal bones-— the sides by that of the frontal and by the os 
planum — and the back parts by that of the ethmoidal and sphenoi- 
dal bones, but with some slight difference of situation and connex- 
ion in different animals.” That, however, which chiefly deserves 
attention is, that it is an imperfect socket The condyle of the 
lower jaw is found, and moving freely, in the postero-lateral part of 
it. A considerable quantity of adeps is also accumulated there ; 
and, interposing between these substances and the eye, is a mem- 
brane or sheath, strong and thick, and thickest at the external and 
superior parts, where the eye would otherwise be exposed, and in 
which direction blows are most likely to fall. 
The Bimana and the Quadrumana. — The food of the Bimana and 
the Quadrumana requires no extraordinary degree of mastication, 
nor is any great length of time employed by either of them in the act 
of mastication. Although the action of the temporal muscle — the 
one most concerned in the comminution of the food — is limited by 
the position of the bony socket of the eye, sufficient room is left for 
the full exertion of all the force that can be required. 
