MORPHOLOGICAL REVISION OF THE SUBORDER. 105 



the bone, and through the upper they gain access to the brain cavity by way of the 

 pituitary fossa. On either side of the single foramen a pair of small foramina carry 

 branches of the internal carotid. All of these foramina are very similar in position 

 to the same ones in Sphenodoii. 



The two articular faces near the anterior end are the basipter>'goid processes. 

 There are no corresponding articular faces on the pterygoid, and it is evident from the 

 specimen No. 1002, where the bones of the palatal surface of the skull are little dis- 

 turbed, that they did not articulate with the pterygoids on their inner side opposite 

 the external processes, as at first supposed, but much further back. It is probable 

 that there was a large mass of cartilage between the basipter>-goid processes and the 

 pterygoid comparable to the meniscus pterygoideiis described by Howse and Swin- 

 nertou in the developing Sp/ioiodon skull. 



The parasphenoid : From between the basipterygoid process extends anteriorly 

 a vertical, compressed plate (plate 18, figs, i and 2, and plate 11, figs. 2 and 3), which 

 extends directly upward in the median line of the skull. The point of union of this 

 plate and the basisphenoid is marked on the upper edge by a deep notch. It has been 

 shown by Parker, Siebenrock, Howse and Swinnerton, and others, that the basi- 

 sphenoid of the adult reptiles is a compound bone, formed of the true cartilaginous 

 basisphenoid and a dermal ossification which is the parasphenoid of the amphibians. 

 In embryonic, and even in early postembryonic life in Spheiiodoii (according to Sieben- 

 rock), the suture between the two is traceable. In the forms with a cartilaginous 

 interorbital septum ( Crocodilia^ Lacertilia^ and Cheloiim) the cartilaginous presphenoid 

 is not ossified, and the parasphenoid extends as a slender styliform process from the 

 anterior end of the basisphenoid beneath the cartilaginous interorbital septum, and 

 supports in embr>'onic life the membranous floor of the pituitary space. There is no 

 doubt that the anterior process of the basisphenoid in the Pelycosauria, as in the 

 Lacertilia and Rhynchocephalia vera, is the renmant of the parasphenoid united to the 

 basisphenoid, and not the presphenoid, as first described by Baur and Case (10). 



The ethmoid: Instead, however, of the parasphenoid process of the Pelycosaiiria 

 ending as a slender rod in the floor of the pituitary space, it extends upward as a 

 strong slender plate, and unites above with a second plate which is in contact with 

 the lower surface of the frontal bones. The suture between the parasphenoid and this 

 plate is closed, but its position is marked by a low ridge, showing the point of coossifi- 

 cation. The upper edge of the upper plate is planted finnly against the under side 

 of the frontals, and there seems to be ample evidence of a direct sutural union ; but 

 as the region is somewhat crushed, it is possible that the plate did not quite touch the 

 frontal in life, but was connected with it by cartilage, and that it has been forced into 

 close contact by the accidents of fossilization. However it may be, the relations of 

 the bone would not be altered. The anterior edge of the plate is irregular and very 

 thin, showing that it passed gradually into the cartilage of the interorbital septum in 

 front. The upper portion of the posterior edge is thin, but the posterior angle is 

 thickened and rounded. There is a deep notch between this angle and the para- 

 sphenoid below, and this notch marks the position of the escape of the second pair 

 of cranial nerves. There is no trace of either orbito- or alisphenoid ossification, as 

 remarked above. 



There is no true median vomer. 



The prevomers : The specimen No. 1002 is of especial value, as it preserves the 

 thin median plates of the skull. It clearly shows the presence of paired prevomers. 

 The prevomers (20) are rather stout rods of bones extending from the middle of the 



