MUSEUM OF COMPARATIVE ZOOLOGY. 



93 



The Brain. 



One of the most interesting features of Aphelops is the very large size of the 



brain. The walls of the cranium are solid. There are no vacuities or air-cells 



in the diploe of the mid-region of the brain- case, such as attain from 1 to 1| 



inches in thickness in Ceratorhinus. Thus the brain is relatively much larger 



Figure 15 —Brain of Aphdopsfossiger X £. Lateral view of intracranial cast. 



than that of the recent rhinoceros, and presents a marked advance upon that of 

 Aceratherium Occident ale. The bulk of the fore- and mid-brain, or the divisions 

 in front of the cerebellum, is approximately as follows : — 



Aceratherium, 420 c.c. Aphelops, 1240 c.c. Ceratorhinus, 720 c.c. 



The bulk of the entire brain is : Aphelops, 1470 c.c. Ceratorhinus, 850 c.c. 

 The relative body weight of the two animals can be roughly estimated from a 

 comparison of the femora as Aphelops 4, Ceratorhinus 3. It thus appears 

 that the steady brain growth of the ungulates during the Eocene and early 

 Miocene periods reached its 

 highest point in some fami- 

 lies of the later Miocene, 

 and was followed by a de- 

 generation. 



The cerebellum in Aphe- 

 lops is small and partly over- 

 hung by the hemispheres. 

 The lateral view of the 

 hemispheres shows a very 

 marked predominance of 

 transverse sulci, which ra- 

 diate from the vertical syl- 

 vian fissure, S, so that in the basal view of the frontal lobes the fissures are 

 antero-posterior. The dorsal surface of the cast is somewhat imperfect, giving 

 an incomplete reproduction of the parietal and occipital regions. The superior 



Figure 16 — Brain of Ceratorhinus Sumatrensis X j. 

 Lateral view of cast. 



