25 



tremities of the pterygoid converge with a gentle curve, convex outwards, to 

 the posterior margin of the osseous palate, and thus form the lateral and an- 

 terior boundaries of the long and wide posterior nasal aperture. The inner side 

 of the pterygoid is moderately convex ; the outer side concave ; the inferior ob- 

 tuse margin being slightly everted. The foramen ovale perforates the middle 

 of the outer side of the pterygoid, nearly two inches from its posterior margin : 

 a ridge is continued from the middle of the posterior edge of the bony palate 

 along two-thirds of the inner side of the pterygoid, about an inch above its in- 

 ferior margin. The canal for the second division of the trigeminal nerve is con- 

 tinued from the foramen rotundum, along the inner side of the root of the pte- 

 rygoid, which separates it by an extremely thin plate of bone from the nasal 

 cavity ; the outlet of the canal is situated about three inches in advance of that 

 which gives exit to the third division of the same nerve. The body of the 

 sphenoid, as it extends forwards into the nasal cavity, contracts to a median 

 ridge, which supports the vomer : on each side of this median ridge, a smooth 

 and concave plate of bone arches down to form the inner side of the pterygoid, 

 and is broken only by a narrow, deep and straight vascular canal, continued from 

 a foramen about an inch anterior to the expanded terminations of the Eustachian 

 depressions. The sides of the base of the cranium are chiefly formed by the petrous 

 or petro-temporal bones, here wedged in between the sphenoid, exoccipital and 

 squamo-temporal bones. The innermost portion of the petrous bone is a sub- 

 compressed, conical protuberance, the blunt apex of which projects downwards 

 into the lateral emargination of the basi-sphenoid and forms the outer and 

 posterior boundary of the canahs caroticus. On the outside of the conical pro- 

 cess the petro-temporal sends down a rugged cubical process, one side of which 

 is towards the cavity lodging the conical process, a second bounds the jugular 

 foramen anteriorly, a third forms the inner side of the rough stylo-hyal cavity, 

 and the fourth, or anterior side, bounds the posterior part of the tympanic 

 cavity. 



The inferior, rugged mastoid protuberance is excavated for the ligamentous 

 articulation of the stylo-hyal bone*. The articular cavity is shallow, of a subcir- 

 cular form, about an inch in diameter, with a well-defined, rugged margin ; its 



• This bone is figured in situ in Plate I. 

 D 



