MORPHOLOGICAL REVISION OF THE SUBORDER. 97 



of the quadrate is rounded and gives attacliment through its length to the quadrato- 

 jugal, but just above where the quadra to-jugal joins the upper surface of the inner 

 condyle the two are separated by a good-sized foramen, 'Ca^ foramen quadratitm. This 

 foramen serves as an important landmark in the skull ; it is not present in the Cotylo- 

 saiiria; it is probably present in all the primitive Archosaiiria { = DiaptosaHria^ Osborn) 

 although it has been demonstrated only in the Pelycosatiria and Rhyticocephalia vera; 

 it is present in the carnivorous Dinosaurs^ the Ichthyosaurs, and the Phytosaurs ; it is 

 absent in the Crocodilia^ the Pterosaurs^ and the Squainata. 



The posterior end of the pter\'goid overlaps the quadrate on the inner side, the 

 lower edge extends back almost to the posterior limit of the bone and is attached to 

 the inner side of the inner condyle. 



The qjiadrato-jugal occupies a relatively unimportant position in the skull. It 

 is a very thin plate of bone, with its lower end and posterior edge attached to the 

 quadrate, as described above. The upper end becomes ver>' sharp and is wedged in 

 between the prosquamosal and squamosal and comes in contact with the parietal. It 

 is separated from any contact with the jugal by the descending process of the prosqua- 

 mosal, as described below, and in turn it separates the prosquamosal from the squa- 

 mosal, thus occupying a unique position among the reptiles. The position of the 

 quadrato-jugal is not anomalous, however, for if the upper end were withdrawn from 

 contact with the parietal by shortening, the prosquamosal and the squamosal would 

 come in contact, and a union of the two would produce the bone called squamosal or 

 squamosal -I- prosquamosal in Sphenodon. 



The prosquamosal has the position usually assigned to the quadrato-jugal; that 

 is, it connects the jugal and the quadrate. It would have been taken for the quadrato- 

 jugal in the present specimens if the presence of the foramen quadratum had not 

 indicated the true position of the quadrato-jugal. (The significance of the position of 

 the prosquamosal is discussed in the description of the temporal region below.) The 

 prosquamosal joins the jugal in about the middle of the inferior temporal arch, the 

 two bones narrowing somewhat as they approach, so the edges of the inferior arch are 

 concave both above and below. Posteriorly the prosquamosal widens, forming an 

 upper and lower process, and the bone becomes roughly T-shaped. The lower three- 

 quarters of the posterior edge join the quadrato-jugal, and the upper quarter joins the 

 anterior edge of the posterior process of the postorbital to form the posterior edge of 

 the superior temporal vacuity. The posterior edge of the prosquamosal passes under 

 the quadrato-jugal articulating with its lower surface, and finally articulates with the 

 edge of the quadrate near the quadrato-jugal. This is shown in specimen No. 1002 

 University of Chicago, and Nos. 4036 and 1826 Am. Mus. 



The bones forming the edges of the superior temporal vacuity are approximated, 

 so the vacuity is very small. In the crushed specimens the sides of the upper vacuity 

 are very close together and it seems that they must have been so in life. In No. looi 

 University of Chicago, the edges of the bones where they would meet are very thin, 

 and it is possible that they met over the vacuity, although there could have been no 

 true articulation even in this case. There is a strong rugosity of the lower ends of the 

 parietal which covers the vacuity, but this I am inclined to regard as pathological. In 

 specimen No. 1002 University of Chicago, Dimetrodon gigas^ the vacuity is open, but 

 very small and narrow. In specimen No. 4036 Am. Mus., labeled by Cope Naosauriis 

 claviger, the vacuity is even smaller, not over 15 mm. long. 



The parietal has a broadened horizontal upper portion which unites by strong 

 suture with the frontal, postorbital, and the parietal of the opposite side, but does not 



