12 THE MORPHOLOGY OF THE SKULL 



leaving the egg.'"" The basioccipital forms the lower portion of the condyle and lies 

 between the exoccipitals and opisthotics. The lower surface is trough-like for its 

 posterior half and supported a posterior extension of the basisphenoid. Laterally a 

 slight notch forms the inner wall of the fenestra ovalis. Anterior to the horizontal, 

 trough-like portion the inferior surface rises sharply ; the angle thus formed is 

 marked by a large foramen of unknown function, perhaps the hypophj'sis passes into 

 the interior of the basioccipital, PI. V, Fig. 3. The petrosals join the opisthotics, 

 exoccipitals and the basioccipital, but the sutures are not distinguishable. The lower 

 part of the anterior edges were continued forward as long processes, the anterior 

 inferior processes of Siebenrock.f These are partially destroyed in the specimen. A 

 deep notch in the anterior edge of the petrosals just above the origin of these pro- 

 cesses, the incisura otosphenoidea Sieb., marks the point of exit from the brain cavity 

 of the fifth pair of nerves (trigeminus). The superior end of the anterior edge is 

 separated from the supraoccipital by a notch which is continued on the sides of the 

 bone as a shallow, short groove. The posterior edge contributes the last portion to 

 the walls of the fenestra ovalis. 



"The basisphenoid remained free. The posterior edge is greatly thickened verti- 

 cally and its lower edge stood well away from the basioccipital. The otic region and 

 the posterior edge of the basisphenoid were covered with a large mass of cartilage. 

 The lower surface of the basisphenoid is excavated by a deep pit, PL V, Fig. 4, which 

 opens on the posterior as well as the inferior surface of the bone and divides the 

 posterior into two parts. The 'upper edge of the posterior surface, forming the base of 

 the pit, was continued backward as a spout-like process articulating with the lower 

 surface of basioccipital. The anterior edge is extended forward as a parasphenoid 

 rostrum originating between the short and stout pterygoid processes. 



" The foramina penetrating these bones are remarkably similar in position to those 

 penetrating the same bones in Sphenodon. The condylar foramen transmitting the 

 twelfth pair (hypoglossus) penetrates the exoccipital just anterior to the edge of fora- 

 men magnum. Its outer end opens in a notch (the incisxira venx jugularis Sieb.) in 

 the side of the exoccipital. A little below and further forward a second and much 

 smaller foramen opens in the same notch ; this may transmit either the ninth or tenth 

 pair of nerves or a minor blood vessel. Passing forward the notch deepens and is 

 very soon converted into a foramen by the adjacent portion of the opisthotic. This is 

 the forameyi venx jugulmia of Siebenrock and transmits the jugular vein and either the 



*Siebenrock, F. : Das Skelet der Lacerta Simonyi Steind. nnd der Lacertiden familie iiberhanpt ; Sitzunberichten 

 der kaiserL Akademie der Wissenschaften in Wien. Matbm. Naturwiss. Classe., ciii, Abth. 1, April, 1894. 

 t Siebenrock, F. : Zur Osteologie des Hatteria-Kopfes, ibid., Bd. cii, Abth. 1, June, 1893. 



