Oipe.i bio [March 16. 



distance ahoiiL hiillas great as the lengtli of the hemisplieres without change 

 of form. Tlic mass then expands laterally and suix-riorlj-, rising upwards 

 on each side of an osseous sejitum, which does not divide the olfactory 

 lohefi to the inferior face. They are thus deeply grooved above, and 

 tinally become furcate near to tlie extremity. Posterior to this point the 

 inferior face rises, and the apices project laterally and forwards from the 

 superior part of the lobe. The olfactory lobes consist, then, of a massive 

 peduncle supporting a grooved subconical enlargement, which is bifurcate 

 at the ai)ex.* 



Since the internal walls of the skull show the foramina for the exits of 

 the cmnial nerves, we have a sufficient basis for the determination of the 

 parts of the brain. In this attempt we are met by the difficulties which 

 are inherent in tiie use of a cast to represent a brain. Although the fora- 

 mina sphenoorbitah and rotundum can be readily fixed, their position is 

 such as to give the point of exit of the uervus trigeminus an unusually in- 

 ferior position. This appears to bo the case to a still greater extent in the 

 Uinlntherium,\ where the lateral descending masses are at tlie .same time 

 not nearly so largely developed as in C'oryphodon. The large inferior area 

 enclosed between these boundaries is then homologous with Wic pons varolii 

 or that part ot the eneephalon which is covered I)y it. Its appearance in 

 Uintatherium supports this identification, but its proportions and anterior 

 position in Coryplwdon depart more widely from the usual form. The 

 two anterior submedian ridges of its surface, faintly indicated in Uinta- 

 therium, may be the homologues of the pronounced median ribs in 

 Voryphodon whicili resemble a continuation of the anterior pyramids of the 

 medulla oblongata. As they are not very distinctly marked in the medulla 

 of Con/phodon, their identification may be uncertiiin, but they look like 

 that portion of the anterior pyramids which is continuous witli the crura 

 cerebri, and which are concealed in ManniKilia by liie pons varolii. Their 

 prominence in Coryphodon indiciUes tliat the pons is wanting in this 

 genus as in the Reptilio.. A shallow concavity of the sphenoid bone be- 

 tween the origins of the trigemini indicates the position of a jiituitary body 

 or hypo])hysis. 



In profile the brain closely resembles in form that of a lizard, e. g., an 

 Ami pa, excepting that in the latter the cerebellum is more elevated. 

 The extension downwards and forwards of the middles brain with its pro- 

 jection below the hemispheres is common to both, but the inferior portions 

 at least, do not appear to be homologous in the two. In the Coryphodon, 

 the lateral projections correspond with the exits of the trigeminus from the 

 skull ; in the Amiva this part terminates in the optic; triicts. The superior 

 portions of the middle Itrain correspond in appearance and relative size 

 with that of the Amiva, but a clear difliculty in identifying them in the 



• Measurements of this brain are given in the article on Coryphodon elephan- 

 i<>l>u.f, in my fc»rllicoininK report on tlio vertebrate Paleontology of New Mexico, 

 Vol. IV, of the report of Lieut. (}. M. Wliocler. 



t Hee Amer. Journ. Hcl. Arts, 1876, pi. iv, p.A&'y. 



