AMERICAN LABYRINTHODONTIDjE 579 



At the infra-basal angle of the skull there is an elongate oval 

 foramen which clearly bears the same relation to its investing bones 

 as does the quadrate foramen in the Ichthyosaurs, and nearly the 

 same relation as in Sphenodon, the parasuchians some of the theropod 

 dinosaurs, and Dimetrodon. On the outside it is bounded by the 

 prosquamosal and quadratojugal; below and on the inside, by the 

 quadrate. In Sphenodon, the parasuchians, theropod dinosaurs, and 

 Dimetrodon the squamosal does not enter into the outer wall of the 

 foramen. Dr. A. S. Woodward figures this foramen, and calls it 

 the posttemporal. 1 The posttemporal in reptiles is bounded on 

 the inside by the exoccipitals and supraoccipitals, below by the 

 exoccipitals or opisthotics or both, on the outside by the squamosal 

 or parietal or by both, and above by the parietal and squamosal. 

 As the relations of this foramen in Anaschisma and Capitosaurus 

 are entirely different from those of the posttemporal foramen in 

 reptiles, it cannot be homologized with that foramen. On a previous 

 page it is shown that another foramen is homologous with the post- 

 temporal foramen of reptiles. As the relations of this opening are 

 almost identical with those of the quadrate foramen in reptiles, it is 

 here considered as homologous with that foramen. 



Case postulates 2 that the quadrate foramen is in its inception 

 in Dimetrodon, but its presence in the Labyrinthodontidas indicates 

 that it is a much more primitive character than he supposed. 



The exoccipitals are expanded in the base of the skull, articulating 

 with the parasphenoid in front, with the' pterygoids on the outer 

 sides, and with each other in the median line. The two condyles 

 form strong projections from the posterior part. Passing upward 

 and slightly forward from near the end of the condyles, there is a 

 strong column which divides at the upper end, one branch meeting 

 a downward projection of the supraoccipitals, the other articulating 

 with the opisthotic. The lateral margins of the foramen magnum, 

 formed by the inner part of the exoccipitals and the downward pro- 

 jections of the supraoccipitals, curve gently outward. Just above 

 the condyle on the posterior inner side of the upward projection of 



1 Loc. tit., p. 172. 



2 Transactions of the American Philosophical Society, 1905, Vol. XXI, Part I, 

 p. 10. 



