72 A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



as the anterior edges of the orbits. Just anterior to the epiphysis of the brain the 

 bones of the two sides meet below, inclosing a long narrow cavity which remains 

 open in front. This sheltered the great elongation of the nasal lobes and the ante- 

 rior portion of the brain shown in Cope's cast. 



Anterior to the basisphenoid and joining the short anterior rostrum is a single 

 vertical plate. This ends somewhat abruptly behind, where it joins the basisphenoid 

 but extends upwards until it touches the alisphenoids above. It remains in con- 

 tact with these bones to their anterior ends and from there forward is joined by 

 cartilage to a prominence on the lower surface of the nasals. The lower edge of its 

 anterior half is in contact with the upper edges of the prevomers. This bone is 

 similar in all respects to that figured by Broom in Lystrosaurus and by the author in 

 Dimetrodon as the ethmoid or true vomer. It is in direct continuation with the 

 parasphenoid rostrum, if it is not an actual part of it. 



The brain: The following account of the brain is transcribed directly from 

 Cope's account (30). 



"The brain-case in the Diadectidce differs from that of the Clepsydropida 

 much as that of the Varanidce differs from those of other Lacertilta. That is, it is 

 continued between the orbits, so as to inclose the olfactory lobes of the brain within 

 osseous walls. These walls are thin; especially at the interorbital region, and in the 

 specimen the anterior extremity is so far imperfect as to leave the form of the 

 anterior fundus in doubt. * * * 



"The formation of the cranial walls requires preliminary notice. In the first 

 place the vestibule of the ear can only have been separated from the brain by a 

 membranous septum, as is the case in the Protonopsis horrida* (Menopoma). In 

 clearing out the matrix no trace of osseous lamina could be detected on either side 

 and the edges of the huge foramen thus produced are entire, and present no broken 

 edges. Anterior to the vestibule, the prootic bone has a small extension, terminating 

 in a vertical border. In front of this is a huge vertical foramen through which issues 

 the trigeminus nerve which is even larger than that found in the Testudinata 

 and CrocodilidcE. The anterior border of this foramen is formed by the probable 

 alisphenoid, whose posterior edge is nearly parallel with the anterior border of the 

 prootic, sloping forwards as it descends. The basicranial axis is thin at their 

 union on the middle line below, and, thickening forwards, is excavated by a rather 

 small conical fossa. Anterior to the fossa is a smaller impressed fossa, and on either 

 side of it, each lateral wall is excavated into a shallow fossa which descends towards 

 it. The frontoparietal fontanelle is of extraordinary size. 



" I. THE BRAIN. 



"When the superior border of the medulla oblongata at the foramen magnum 

 is placed horizontally, the axis of the brain ascends at an angle of 45 towards the 

 frontoparietal fontanelle. The superior surface, anterior to the foramen magnum, 

 is subquadrate in outline, the angles being truncated, and directed anteriorly, 

 posteriorly, and laterally. A posterior constriction connects it with the medulla; 

 and an anterior one defines the middle brain and hemispheres. Each lateral 

 truncated angle represents the foramen of the trigeminus nerve. The space thus 

 bounded is divided into two nearly equal areas by a transverse groove, which extends 

 from the posterior edge of one of these foramina to the other. The posterior of 

 these I suppose to represent the cerebellum, and the anterior the optic thalami. 

 The cerebellar surface indicates that, as in many lizards, the cerebellum is simple, 

 and very slightly convex. 



* See Journal Academy Philadelphia, 1866, p. 105, where the characters of the skull in the JJrodela are pointed out . 



