24 



verse direction. It is bounded by a well-defined almost sharp ridge, which 

 encroaches for about the third of an inch upon the outer extremity of the 

 smooth articular surface, forming there a rough angular rising. The inner sur- 

 face of each condyle is, as it were, cut down vertically to the sides of the 

 occipital foramen, and is also slightly hollowed, so that the inner margin of 

 the articular surface somewhat overhangs it. 



The posterior margin of the broad basi-occipital plate, forming the lower 

 boundary of the foramen magnum, presents an obtuse angular excavation. The 

 under surface of the plate is flat : it is pierced by a small vascular foramen (a) 

 immediately anterior to the condyle ; and the large anterior condyloid foramina 

 (6), each half an inch in diameter, open obliquely upon the sides of the basi- 

 occipital, about half an inch from the condyles : the hone is continued, external 

 to these, into a short but strong rough tuberosity, forming the posterior boundary 

 of the articular depression (c) for the stylo-hyal bone, and the external boundary 

 of the jugular foramen (d), which is immediately anterior and external to the 

 anterior condyloid foramen. The sides of the basi-sphenoid begin to descend 

 below the level of the intervening plate, rendering it concave transversely, and 

 terminating each in a rough subelliptical tuberosity (/), placed with its long 

 axis almost transversely, its extremities being pointed, and the inner ones over- 

 arching, in the reversed position of the skull, the narrow, smooth, intervening 

 surface of the sphenoid. In the antero-posterior direction, the sphenoid, as it 

 extends forwards into the posterior wide opening of the nasal cavity, is slightly 

 convex. The sides of the basi-sphenoid, immediately anterior to the jugular 

 foramen, are excavated and give lodgement to the obtuse inferior apex of the 

 loosely articulated petrous bone which divides the jugular from the very small 

 carotid foramen. The transverse protuberances above described, are the seat 

 of large air-cells, which do not communicate with the tympanic cavity ; they 

 are laid open on the right side in the plate. The bony canal for the Eusta- 

 chian tube is narrow at its commencement, but rapidly expands near its com- 

 munication with the posterior nasal aperture ; it divides the sphenoid protube- 

 rance from the pterygoid bones. These are anchylosed, as processes, to the 

 sphenoid, and consist on each side of a moderately thick, long, vertical plate 

 of bone, about three inches in depth at their posterior part, which is the 

 thickest, and is roughened by vertical ridges and furrows. The anterior ex- 



