THE SKULL. 231 



along the inner wall of the orbit, close to its 

 dorsal border, to the foramen by which the 

 two nerves leave the orbit : this is situated 

 at the antero -superior angle of the orbit, and 

 has already been seen on the dorsal surface 

 of the skull. 



c. The articular surface for the hyo-mandibular car- 



tilage is a concave depression on the side of 

 the hinder end of the skull, below the auditory 

 capsule. 



d. The post-orbital groove is a deep horizontal groove 



immediately above the articular surface for the 

 hyo-mandibular cartilage, and overhung by the 

 projecting ledge of the auditory capsule which 

 lodges the horizontal semicircular canal : it 

 lodges during life the venous canal through 

 which the orbital sinus communicates with the 

 anterior cardinal sinus. 



The anterior end of the groove is bridged 

 over by stout ligamentous tissue. 



e. The foramen for the glosso-pharyngeal nerve is at 



the hinder end of the floor of the post-orbital 

 groove, behind and below the horizontal semi- 

 circular canal of the ear. 



4. The ventral surface of the skull. 



a. The base of the skull is a broad flat plate of 



cartilage, crossed almost transversely a little 

 behind its middle by a pair of grooves in which 

 the carotid arteries he. At the point of meeting 

 of the grooves in the middle line is an aperture 

 through which the internal carotid artery enters 

 the skull. 



b. The apertures of the olfactory capsules are large, 



but. are considerably reduced by the nasal car- 

 tilages, which are liable to be torn in cleaning 



