42 OSTEOLOGY OF THE HORSE. 



INTERNAL PARTS: 



Comprehending the Cavities of the Cranium, Orbit, Nose, and 

 Mouth. 



I. — CAVITY OF THE CRANIUM, 



Constructed for the lodgement of the brain with its appen- 

 dages : is in form ovoid, flattened inferiorly, broader anteriorly 

 than posteriorly ; its antero-posterior or long diameter measuring 

 about seven inches ; its transverse or lateral diameter, about four 

 inches ; its vertical or perpendicular diameter, about three and a 

 half inches. At the same time it is to be observed, that, although 

 the general form of the cavity is the same, its dimensions may and 

 do vary in different heads. The eight bones composing the cranium 

 all present internally surfaces more or less concave, which, united, 

 form the cavity under consideration ; hence it is that the interior is 

 not regular or uniform, but presents to view different hollows, 

 which are adapted to distinct prominences of the cerebral mass. 



DIVISION of the interior surface into roof and base of the 

 cranium : — 



The roof is formed by the frontal, parietal, and occipital 

 bones : its superficies is larger than the extent of the base, and it 

 is without any apparently defective places, observable in the 

 latter. It presents — 1st, On the mesian line, from front to back, 

 the sagittal groove, for the longitudinal sinus, formed by the 

 frontal and parietal crests, crossed towards the front by the co- 

 ronal suture, and bounded posteriorly by tlie parietal protuberance, 

 to which is attached the tentorium, and behind which is the occi- 

 pital cupula, for covering the cerebellum. — 2d, On either side, 

 along the same line, the cerebral concavities of the frontal bone ; 

 the coronal suture, the boundary line between them and the 

 parietal concavities ; the transverse grooves, for the lateral sinuses j 

 and, sunk within them, tlie lambdoidal suture. 



The base is formed by the temporal, sphenoid, ethmoid, and 

 occipital bones. It presents — 1st, on the middle line, from before 

 hdickwdivAs, the crista gain, and on its sides the ethmoidal fossa and 

 cribriform plates, bounded laterally by the internal 07-bital plates 

 of the frontal bones, and them pierced by the internal orbital 

 foramina; the concave surf ace of the body of the ethmoid bone ; 

 the optic hiatus leading to the optic foramina ; a transverse 

 suture between the ethmoid and sphenoid bones. Upon the 

 sphenoid bone, the pituitary fossa, bounded laterally by the two 

 optic fossa; the latter leading to the foramina lacera orbitalia, 

 over which are the spinal foramina : a transverse elevated line 

 denotes the place of junction of the sphenoid with the occipital 

 bone. Belonging to the occipital bone, are the basilar fossa and 



