390 Bullet in. American Museum of Natural History. [Vol. XXVII, 



brained form, which in all its dental and skeletal characters would fall under 

 the Condylarthra as here defined. 



Muzzle lieavij, forehead very broad. This is a universal character of the 

 Lower Eocene Perissodactyls and is a direct inheritance from the Condy- 

 larth condition. 



Post-orbital constriction rather marked. Another very primitive (Condy- 

 larth) and strongly marked character (seen especially in Eohippus). Its 

 meaning is that the small brain was still largely confined to the ])arietal 

 segment and that the anterior portion of the cerebrum, i. e. the frontal lobes, 

 had not yet broadened and pushed forward against the anterior wall of the 

 brain case. 



Face larger thayi cranium. Seen in Eohippus, Isectolophus, Hyrachyus 

 and others {cf. Condylarthra). 



Skull moderately dolichocephalic, i. e., about as in Eohippus and Isecto- 

 lophus (cf. Condylarthra). 



Occiput high and narrow. Seen in Eohippus, Heptodon and others. 

 Occipital crest slender not flaring {cf. Phenacodus wortmani). 



Zygomata slender (as in Eohippus) (cf. Phenacodus tvortmani). The 

 very stout zygomata, high sagittal crest and flaring occipital crest in the 

 Middle Eocene Palceosyops are possibly a secondary result of extreme 

 brachycephaly and heavy jaws and canines. Zygomatic process of maxil- 

 lary extending outward below malar. 



Orbit bounded by small post-orbital processes both on frontals and 

 nialars. 



Proportions and relations of premaxillaries, maxillaries, lachrymals, 

 nasals and frontals prol)ably much as in Euprotogonia. In the orbital 

 region, maxillaries overlapping nasals and overlapped by frontals and 

 lachrymals; in the lateral aspect, a slight anterior narial sinus above max- 

 illaries. Nasals not reaching forward quite as far as the premaxillaries 

 (Eohippus, Isectolophus, the most primitive Titanotheres, etc.), cf. Phena- 

 codus wortmani. Lachrymal with small tubercle, spreading out on the 

 orbit internally, partly extending on face, duct marginal to internal. 



Ascending ram.us of mwidible and coronoid, large; areas for temporal 

 and masseter muscles relatively large (cf. Condylarthra). 



Cranial foramina conforming strictly to the Condylarth-Creodont plan: 

 i. e., optic and rotund foramina distinct from the foramen lacerum anterius; 

 an alisphenoid canal; large foramen ovale piercing alisphenoid at some 

 little distance back of the alisphenoid canal and just internal to the glenoid 

 fossa; postglenoid foramen not conspicuous; sphenopalatine foramen nor- 

 mal; median and posterior lacerate foramina confluent, owing to the small 

 size of the petrosal and tympanic, which had not coalesced. Osseous au- 



