42 



THE HISTORY OF THE PELYCOSAURIA, WITH 



sphenoidea by the membranous wall of the anterior portion of the brain case, as in Sphe- 

 nodon and many lizards (Fig. 5, 6). 



The deep pit excavating the lower surface of the basisphenoid is in all probability 

 the lower opening of the Eustachian tubes. In most reptilian forms the tubes pass into 



Fig. 4. Side view of a cast of the brain cavity. 



Fig. 5. Lower view of the basisphenoid. 



Fig. 6. Lower view of the cranial region. 



Fig. 7. Lower view of the cast of the brain cavity. 

 5. The trigeminus nerve. 7. The facial nerve. 12. The hypoglossus nerve. Ju. The jugular foramen. 

 Ty. Cast of tympanic cavity. Hy. Hypophysis. Sy.F. Foramen penetrating base of basioccipilal. F.O. Fenestra 

 ovalis. I. C. Foramina for internal carotids. Eu. Opening of eustachian tubes. Ob. Cerebellum. 



the pharynx in the neighborhood of the basioccipital-basisphenoid suture and anterior 

 to the fenestra ovalis. In the Crocodilia and the aglossal batrachians they have a common 



