44 THE HISTORY OF THE PELYCOSAUBIA, WITH 



The hypophysis is the most interesting feature of the brain. Descending between the 

 anterior inferior process of the petrosal and turning posteriorly, it occupies a small 

 notch in the posterior edge of the upper surface of the basisphenoid and then passes 

 directly into the body of the basioccipital through the foramen mentioned. In the 

 Crocodilia a somewhat similar condition exists. The basisphenoid is excavated for a con- 

 siderable extent to accommodate the hypophysis. This makes it probable that the exca- 

 vation of the bone is merely a secondary character to make room for the hypophysis, 

 for in the Crocodilia the basisphenoid takes a large part in the floor of the brain-cast, and 

 in the present form it is pushed so far downwards that it is excluded and the hypophysis 

 encounters the basioccipital as soon as it turns toward the rear. 



Marsh 64,65 has described in the family Atlantosauridce of his suborder Sauro- 

 poda of the Dinosauria a condition in which the pituatary cavity becomes a canal 

 perforating the basisphenoid and opening into the pharyngeal cavity, considering it an 

 embryonic character such as exists in the chick at the fifth day of incubation. 



If the hypophysis occupied the entire cavity in the basioccipital it extended back 

 nearly as far as the tympanic region and much further back than in most reptilian 

 forms. In Sphenodon, the Crocodilia and some amphibians it reaches well back, but 

 not so far as in the present form. 



Compared with Sphenodon, the specimen shows the following points of resemblance. 

 The foramina for the blood vessels and nerves are almost identical in position and nature. 

 The contour of the medulla and cerebellum was similar and the hypophysis extended 

 far back. The only point of difference is the excavation of the basioccipital to receive 

 the distal end of the hypophysis. The free communication of the tympanic cavity is 

 a character which is found in many existing primitive forms and is of secondary impor- 

 tance. 



The points here brought out confirm the close relationship of Pelycosauria to the 

 primitive Rhyncocephalia already asserted by Baur and Case. 28 



The Palate. 



The following elements of the palatal region are preserved : both the pterygoids (the 

 left nearly complete), the palatine of the left side, lacking the posterior portion and parts 

 of the right one. No traces of the vomers have been found. 



The pterygoids (PL I, Figs. 15, 16) are large bones which show three processes ; an 

 anterior horizontal one, becoming very thin in front and underlying the palatines ; a 

 posterior one, forming an extensive vertically expanded plate, and an external very mas- 

 sive ectopterygoid portion. The posterior plate leaves the massive part by a roundly 

 trihedral neck ; its lower edge runs downwards and backwards to the quadrate. The upper 



