MORPHOLOGICAL REVISION OF THE SUBORDER. 99 



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. 



"Thebasisphenoid remained free. The posterior edge is greatly thickened ver- 

 tically, 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, plate 11, fig. 2, 

 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 the basioccipital. The anterior edge is extended forward as a para- 

 sphenoid 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 

 foramen magnum. Its outer end opens in a notch (the incisura vence jiigiilaris 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 verj' 

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

 foramen vence jitgularis of Siebenrock and transmits the jugular vein and either the 

 ninth or tenth nerves or both of them. In Sphenodon the foramen transmits not only 

 these but the twelfth pair as well, the nerves being separated from the vein by very 

 thin walls of bone and may be separated from each other or have a common canal. 

 The opening of the twelfth pair into the notch which forms the beginning of the 

 jugular foramen is then very similar to the condition found in Sphenodon. 



"The fenestra ovalis is a single opening leading by a very short canal directly 

 into the brain cavity, a character found in fishes and the amphibian Menoponia and 

 existing imperfectly in some recent reptilia, as the turtles. The same thing is 

 described by Cope as existing in another Permian reptile, from the same horizon as 

 the present specimen, but belonging to a separate family, the Diadectido', and his 

 order Cotylosauria. 



" The foramina for the seventh (facial) pair of nerves appear on the outer surface 

 of the petrosal just anterior to the fenestra ovalis. They are located relatively a little 

 further back than in Sphenodon. On the inner face of the same bone the foramina 

 appear at the side of the base of the brain cavity a little anterior to their external 

 opening. They are located just anterior to a slight ridge which defines the limits of 

 the tympanic cavity. In Sphenodon this is about the point of location of a foramen 

 common to the seventh and eighth nerves, which, however, almost immediately 

 divides, the posterior branch penetrating the inner wall of the tympanic cavity and 

 leading the auditory nerve to the inner ear. 



" The foramen for the fifth (trigeminus) nerve is completed from the incisura 

 otosphenoidea by the membranous wall of the anterior portion of the brain case, as in 

 Sphenodon and many lizards. 



" A cast of the brain cavity shows fairly well all parts posterior to the fifth pair 

 of nerves, and the hypophysis anterior to them. As is well known, the brain in the 



