I04 REVISION OF THE PELYCOSAURIA. 



portions, but the anterior parts come close together. From the inner edges of the 

 anterior portions of the pter>'goids vertical plates extend upward in the skull, forming 

 a median septum in the lower part of the nasal region. Anteriorly these plates unite 

 and below they pass into the prevomers. The suture between the plates and prevomers 

 is visible anteriorly, but posteriorly it disappears (figs. 30 and 31, and plate 18, fig. i, 

 pt). Similar vertical plates occur on the inner edge of the pter} golds of Protersuchits 

 fergusi Broom. The median portions of the anterior processes were covered with 

 small teeth that were in part, at least, implanted in shallow sockets. 



The median external process is a stout projection with a flat external face, which 

 formed a buttress for the lower jaw, such as occurs in the Crocodilia and in Sphenodon. 

 It stands much nearer the surface of the skull than in the forms mentioned, so that 

 its outer face is in almost the same plane as the side of the skull. The upper and 

 anterior portion of the external face of this process is certainly formed by the trans- 

 verse, and it is marked by a sculpture of fine lines. The lower edge of the process 

 is rounded, and carries a row of teeth in sockets. The number and size of these 

 teeth vary, and so seem to be of value in specific determination. 



The posterior process is a broad plate standing nearly verticalh- in the skull, but 

 inclining inward somewhat at the top. kX. the point of departure from the median 

 process it is of less vertical extent and stouter, but as it passes back it becomes very 

 thin and plate-like. It joins the quadrate as described abo\'e, and from its upper 

 surface rises the epipterygoid. 



The epipterygoid is the only bone that does not have a complete representation 

 in one of the three sktills. In No. 1002 the lower ends are still in contact with the 

 pterygoid, but the upper part is lost. It seems that the bone articulated loosely with 

 the parietal by the intervention of cartilage, much as in Sphenodon. The form was 

 that of a slender flattened pillar. 



The palatines are slender plates closely attached to both the maxillaries and 

 pterygoids. The attachment to the maxillary is voxy firm. A vertical expansion of 

 the bone is applied to the inner side of the alveolar edge, and from this springs the 

 horizontal plate. The bone reaches from the posterior end of the maxillary to a point 

 opposite the canine tooth. The anterior end forms the posterior edge of the posterior 

 nares. 



The basi sphenoid \s best shown in plate 11, figs. 2 and 3. The posterior end is 

 swollen, and articulates with the basioccipital. There is evidence of the presence 

 of considerable cartilage in this region during life. On the lower surface there is a 

 deep pit, and near the anterior end two strong articular faces. The anterior end 

 terminates in a strong, median, vertical plate, the parasphenoidal rostrum. 



The deep pit excavating the lower surface of the basisphenoid is, in all proba- 

 bility, the lower opening of the Eustachian tubes. In most reptilian forms the tubes 

 pass into the pharynx in the neighborhood of the basioccipital-basisphenoid suture 

 and anterior to the fenestra ovalis. In the Crocodilia and the aglossal batrachians they 

 have a common opening into the mouth. In the present forni the tubes probably 

 penetrated the large mass of cartilage covering the otic region and the posterior end 

 of the basisphenoid and found a common opening in the deep pit described. It is 

 difficult to imagine the use of such an extensive cavity in the basisphenoid, but in 

 the Teleosauria an equally large cavity is found roofed over with bone. Anterior to 

 this pit two foramina penetrate the lower surface of the basisphenoid bone, and on its 

 upper surface a large foramen appears just posterior to the origin of the parasphenoid 

 rostrum. Through the pair on the lower surface the internal carotid arteries enter 



