MUSEUM OF COMPARATIVE ZOOLOGY. 



87 



nection between these American genera and the A mphitragulus, Dremotherium, 

 etc. of St. Gerand le Puy is obvious from the most superficial comparison. 



The collection contains specimens probably indicative of other species of 

 Cosoryx, some of them much larger than C. furcatus ; but in the absence of asso- 

 ciated teeth, it is not possible to refer them to their proper categories. 



PERISSODACTYLA. 



ANCHITHERIIDuE. 

 MESOHIPPUS, Marsh. 



The Brain. 



Mesohippus had a large and well convijluted brain. The length and breadth 

 indicate that it weighed about one third as much as the brain of the recent 

 horse, while if we estimate the body weights of the fossil and recent animals by 

 the relative size of the humeri, the brain of the Miocene species was proportion- 

 ally heavier. The cerebrum 

 of the horse is, however, 

 much more highly convo- 

 luted, and the frontal lobes 

 are relatively broader. The 

 MesoJiijypics brain is distin- 

 guished in a mai'ked manner 

 by the longitudinal direction 

 of the parietal and occipital 

 sulci, and by the deep trans- 

 verse frontal sulci, as con- 

 trasted with the oblique sulci 

 of all recent unsculates. In 

 fact, in this respect it bears a 

 marked general resemblance 

 to the brain type of recent 

 Carnivora, and conforms with 

 the higher Ungulata of the 



Figure 10. — Brain of Mesnhippns Bairdiix f. 

 above, and from side. 



From 



Eocene. 



On either side of the lon- 

 gitudinal fissure is a long deep fissure forking anteriorly and marking off the 

 median gyrus, m, of the parieto-occipital region. Parallel with this is a short 

 fissure, which separates the two medilateral gyri, ml, ml'. The third fissure 

 extends to the posterior transverse, and thus entirely separates the supersylvian 

 gyrus, ss, from the medilateral. The fourth fissure is shallower. There are 

 three transverse frontal fissures (Fr. 1, 2, 3) which divide this lobe into three 

 gyri ; the median fissure extends almost to the longitudinal fissure, and sug- 



