OF THK PELYCOSAIKIAN CiKNl'S DIMKTRODON. 19 



The transverse : Heretofore the transverse has not been recognized in any speci- 

 men but in numbers 1001 and 1 002 its presence and relations are readily seen. On 

 the inner side of the jugal as described above and shown in figure] 3 a strong ridge 

 extends forward and receives into its bifurcated end the upper end of the transverse, 

 from this point the transverse extends straight downward on the anterior and outer 

 face of the outer process of the pterygoid ; its lower edge fuses with the pterygoid so 

 that it is impossible to describe its lower limit exactly but it does not extend very far 

 down on the pterygoid. The anterior edge of the transverse unites with the posterior 

 end of the maxillary so that it is held firmly in its position. 



The pterygoid: The pterygoid as repeatedly described has a distinct tripartite 

 form, consisting of an anterior horizontal portion, a median vertical process and a 

 posterior portion which joins the quadrate. Tlie form of tlie bone is best shown in 

 figures 6 and 7, PI. V, which are from specimen 1. 



The anterior plate is separated from the maxillary by the palatine and the trans- 

 verse, the bones join the pterygoid directly so that there are no palatine vacuities in 

 the posterior part of the palate. The anterior processes come very close together in 

 the median line but it is impossible to say whether they are united throughout their 

 length or not ; it seems probable that there was a space between the posterior portions 

 but the anterior parts come close together. From the inner edges of the anterior por- 

 tions of the pterygoids 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 pre vomers is visible 

 anteriorly but posteriorly it disappears. (Figs. 4 and 5, and PL IV, Fig. 1, pt.) Sim- 

 ilar vertical plates on the inner edge of the pterygoids of Proterosuchiis fergusi Broom. 

 See Fig. la, page 26. 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 transverse 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 vertically in the skull but 

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

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



