128 Mammalia. Nervous System, 



hemispheres are devoid of sulci {e.g. Sorcx, Talpa, Erinaceus). 

 The RMnencepliala are long, large, and pyriform. 



iv. Cheiroptera present the same type of brain as the Insectivora, 

 except that the cerebral hemispheres present a few simple folds on 

 their exposed surfaces. 



V. Rodentia also, have a similar brain to the Insectivora, except 

 that the lateral lobes of the cerebellum are larger relatively to the 

 median lobe (esp. in Hare), though that still retains its large size. 

 The cerebellum is as a vrhole proportionally greater to the rest of 

 the brain in liodentia than in other Mammals. The anterior pair 

 (nates) of the corpora quadrigemina are larger than the posterior. 

 The cerebral hemispheres in the smaller species {e.g. Lepus, 

 Cavia) have only a very few shallow depressions ; they do not 

 always, though generally {e.g. Lepus, Castor), leave the corpora quad- 

 rigemina exposed. The cornu ammonis and corpus fimbriatum are 

 usually found very large : and the corpus callosum is of greater 

 relative extent than in Insectivora. 



vi. Sectorialia. Membranes. For the ossification of the tentorium, 

 see Osteology, sub. Sectorialia. In seals both the tentorium and 

 hind part of the/a/.r are ossified, and a thick ridge enters the fore 

 and under part of the falx between the rhinencephalic fossae. JEpen- 

 cephaloji. The cerebellar hemispheres are more highly organised than 

 in the Rodentia : the smallest species have the smallest lateral lobes 

 in proportion to the middle one. Mesencephalon. The posterior 

 pair (testes) of the corpora quadrigemina are the larger. Prosence- 

 phalon. The cerebral hemispheres extend over part of the cerebellum : 

 in many of the Sectorialia they exhibit nothing more than a few 

 shallow grooves. In the Dog, Otter, and Seal, the convolutions are 

 far more numerous than in the feline tribes. The corpus callosum 

 is connected with the fornix by a septum lucidum. 



vii. Prohoscidia. In the TJngulata the relative size of the lateral 

 lobes of the cerebellum increases with the bulk of the species, and 

 attains its maximum in the Elephant. This genus is remarkable for 

 a well developed cerebrum overlapping part of the cerebellum, and 

 for the excess of convolutions on the cerebral surface. 



viii. Perissodactyla. The cerebrum always extends over part of 

 the cerebellum. In the Solidimgula the cerebral convolutions are 

 more numerous than in the majority of Sectorialia : the ' nates ' 

 exceed the testes in size. 



ix. Hyracoidea. The cerebral hemispheres present but few and 

 simple fissures. 



