Nervous System Special. 129 



X. Artiodactyla. In Muminantia the nates exceed the testes in 

 size. 



xi. Cete. The olivary bodies are not covered by a * trapezoid ' 

 layer of fibres. The brain is remarkable for its rounded form, and 

 for the proportional size of the cerebellum, especially of its lateral 

 lobes : the pons is large and prominent. The cerebral hemi- 

 spheres are highly organised in the Dolphins ; the sulci are very 

 numerous. 



xii. In-Enamellata. The cerebellum is not covered by the 

 cerebrum ; its vermiform portion is considerable. The corpora 

 quadrigemina are not reached by the cerebral hemispheres. The 

 smaller and especially the insectivorous species have smooth low tri- 

 angular hemispheres, with small corpus callosum. 



Impl AGENT ALIA. The Prosencephalon presents the following 

 differentiating characters*: 



(.) A peculiar arrangement of the folding of the inner wall of 

 the cerebral hemisphere : a deep fissure, with corresponding pro- 

 jection within, continued forwards from the hippocampal fissure, 

 almost the whole length of the inner wall. In other words, a 

 hippocampus major (instead of being confined, as it is at least in the 

 higher forms of Placental Mammals, to the middle or descending 

 cornu of the lateral ventricle), extending up into the hodij of the ven- 

 tricle, and constituting its inner wall. 



(5. ) An altered relation (consequent upon this disposition of the 

 inner wall) and a very small development of the upper transverse 

 commissural fibres (corpus callosum). 



{c.') A great increase in amount, and probably in function, of the 

 inferior set of transverse commissural fibres (anterior commissure). 



xiii. Marsupialia. Epencephalon. The Cerebellum presents trans- 

 verse convolutions, few in the climbing Koalas and Opossums, more 

 numerous in the locomotive Kangaroos : it is remarkable for the 

 large proportional size of the median or vermiform lobe as compared 

 with the lateral lobes, and the concomitant diminution of the 

 ' Pons'. In nearly all there is a small, subspherical, lateral process or 

 appendage more or less projecting and sometimes lodged in a peculiar 

 fossa of the petrosal above the internal meatus. Mesencephalon. In 

 most Marsupials (Dasyurus, Didelphys) the corpora quadrigemina 

 are more or less exposed between the Cerebrum and Cerebellum. 



Flower. Phil. Trans. 1865, p. 647. 



