is occupied by the carotid artery, the upper and anterior 



portion being occupied by the jugular vein. 



Let us turn again to the posterior aspect of the skull. 

 Immediately lateral to the posterior aperture of the carotid 

 canal the pterygoid articulates with the suspensory ramus 

 of the quadrate [11] and with that ramus shares in forming 

 the inferior boundary of the aperture of the acustico-jugular 

 cavity, the inner portion of the inferior and the medial 

 boundary are formed by the exoccipital bone. Laterally 

 the cavity is widely open to the post-tympanic notch [73.] 

 The tympanic cavity is divided into two portions, con- 

 nected by a canal which occupies the columella sulcus (see 

 Fig. 31) the outer of these (pars lateralis cavi tijmpaniei) 

 is lodged in the tympanic fossa of the quadrate, deepened 

 above and behind hy the squamosal, and in front and below 

 by the quadra to-jugal. The infra-tympanic spine on the latter 



otic ramus of the quadrate, forming thereby a very incom- 

 plete bar across the post-tympanic notch. The inner por- 

 tion of the tympanic cavity (pars nwilialis cavi t ipnpanici) 



to Hoffman (3) Hasse has designated the whole of this 

 cavity " recessus cavi tump i»/ci," even if the cavity were 

 only tympanic it appears that it would be misleading to 

 designate it so, since the tympanic portion is not a recess 

 of that cavity, but lodges the stapedial end of the columella 

 and has both the fenestra? in its inner wall; moreover, this 

 is the only portion of the bony tympanic cavity constantly 

 present in the reptilian skull. 



In the occipital region the floor of the cranial cavity is 

 evenly concave, passing insensibly into the lateral wall 

 where this is formed by the exoccipital bone, and here, 

 close to the floor are the internal apertures of the hypo- 

 glossal canals (canales hijpoglossi) (Fig. 48) [53]. Immedi- 



