44 



THE HISTORY OF THE PELYCOSAURIA, 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 hasisphenoid and then passes 

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

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

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

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

 for in the Crocodilia the hasisphenoid 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 hasioccipital as soon as it turns toward the rear. 



Marsh 64 '® lias described in the family Allantosaurida: of his suborder Sauro- 

 poda of the Binosauria a condition in which the pitnatary cavity becomes a canal 

 perforating the hasisphenoid and opening info 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 hasioccipital it extended back 

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

 forms. In iSpkmod on, the Crocodilia, and some amphibians it reaches well hack, 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 hasioccipital 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 dose relationship of Pelycosauria to flu; 

 primitive Jihyncocephalia already asserted by Banr 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 (PI. 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 



