i8 



AMERICAN PERMIAN VERTEBRATES 



each posterior angle (see Fig. i) there begins a distinct groove, 

 including the pit mentioned by Case in Diadectes, running forward 

 and inward on each side of the pineal vacuity, and on the frontal 

 and nasal bones. Opposite the postorbital angle there is a branch 

 leading outward, and the two main branches seem to meet in a 



pit in the middle of the frontal 

 bone, with a branch, or a dis- 

 tinct groove leading forward on 

 the anterior part of the nasals. 

 That these are mucous grooves is 

 of course possible, but I suspect 

 that they are, rather, grooves for 

 the passage of veins beneath a 

 heavy corneous plate which 

 covered the whole of the upper 

 surface of the skull. 



The relations of the skull 

 bones, so far as they have been 

 reconstructed, of course, are very 

 positively shown, since all, save 

 the dermoccipital, were wholly 

 separated at their sutures. 

 These relations I show in the 

 accompanying outline figure as 

 placed in one plane, that is, 

 without the foreshortening of 

 the decidedly convex profile. 

 See, also, The frontal bones, very strong- 

 ly sculptured, are broader and 

 thicker posteriorly, and give articulation on their outer sides to the 

 prefrontal and postfrontal, which unite with each other, excluding 

 the frontal from the margin of the orbit. The nasal bones, nearly 

 as long as the frontal, have the general roughening of the skull 

 surface, with a single groove on the upper side, obsolete anteriorly. 

 The prefrontal is short, and it extends but little in front of the 

 orbit, articulating with the nasal and, more broadly on the outer 

 side, where it curves downward, with the lachrymal, which extends 



Fig. i. — Nothodon lent us Marsh. Dia- 

 grammatic outline of bones of top of skull, 

 about one-half natural size. 

 Plate XL. 



