24 Field Columbian Museum — Geology, Vol. II. 



tin' bone comes in contact with the proximal end of the vomer ; for a 

 little distance in front of this emargination, and distad to the pointed 

 extremity of the bone, the border is slightly thickened for union with 

 the vomer. Posteriorly, the rounded extremity of the bone is slightly 

 thickened, and with sutural roughening for union with the ectoptery- 

 goid process of the pterygoid. The outer border is slightly concave 

 throughout nearly its whole extent ; it is also thin for nearly its whole 

 extent. Anterior to the small narial emargination, the bone forms a 

 long, slender point. On the proximal end, the thin border is under- 

 lapped by the thin anterior prolongation of the ectopterygoid for a 

 distance of about fifty millimeters ; the remainder of the extent comes 

 in contact with the maxilla, but presents no distinct sutural surface, 

 unless it be near the anterior extremity. There is no posterior pala- 

 tine foramen. 



The ectopterygoid or transverse bone is of a slender, triangular 

 shape. Its slender anterior end extends forward on the outer margin 

 of the palatine. *The posterior inner angle has a well marked sutural 

 surface underlapping the pterygoid process. The outer extremity is 

 thickened, curving somewhat downward to unite with the jugal, and, 

 by a thin border, with the maxilla. 



The vomer is a very long, narrow bone, uniting with the palatine 

 process of the pterygoids posteriorly by a squamous suture, and, for 

 a short distance on the outer side posteriorly, with the slender 

 pointed extremity of the palatine, the small narial opening intervening. 

 They lie closely side by side, apparently without sutural union. 

 They are concave above, and convex below from side to side, and are 

 rather stout. The anterior ends are so concealed that they can not 

 be described or figured. 



Brain-o'ase. — The lateral walls of the brain-case in the reptilian 

 skull are composed of six distinct elements, according to the views of 

 some comparative anatomists. Two of these may be fused with con- 

 tiguous elements in the adult skull, or one or more of them may be 

 entirely absent. Those elements supposed to contain the otic capsule 

 were called by Huxley, in his lectures on the structure of the verte- 

 brate skull (Elements of Comparative Anatomy, 1864), the epiotic, 

 prootic and opisthotic. The other three are the supraoccipital, 

 exoccipital and alisphenoid. The epiotic, Huxley homologized with 

 the so-called epiotic of fishes and batrachians, and, although indis- 

 tinguishably united with the supraoccipital in all adult reptilian 

 skulls*, he believed to be a distinct ossificatory element. This has 



♦Parker describes the epiotic as a distinct element in T>vf>i<ioitoti<s natrix. Phil. Trans.. 

 l^7V l>. 4°S- 



