98 



ANATOMY OF VERTEBRATES. 



Braiu of Mole. 



two pairs is exemplified in fig. 73, />, Didelphys, and fig. 75, B, 

 Pliascolomys, in the Marsupial order ; by fig. 79, Lepus, and fig. 80, 

 8, 9, Cavia, in the Rodentia ; and by fig. 67, Talpa, in the Insecti- 

 vora. Both Z?/- and Liss-enccphala manifest their inferior posi- 

 tion in the present class, and affinity to oviparous Vertebrates, by 

 the larger proportion of the mesencephalon (fig. 46, o) to the pros- 

 enccphulon, than in Gyrcncephala. In most Marsupials (Dasy- 

 urus, fig. 72 ; Didelphys , fig. 73), in many Rodents 

 (fig. 81, Lepus ; fig. 80, Castor), in all Insectivores 

 (fig. 76, Rliynchocyon), and in Bats, the bigeminal 

 bodies are more or less exposed between the cere- 

 brum and cerebellum. As in Amblyopsis (vol. i. 

 p. 278, fig. 175), so in Talpa, the optic lobes, fig. 67, 

 c, do not show a reduction of bulk commensurate 

 with that of the visual organ ; yet there is a de- 

 gree of such relationship in Mammals. Thus the 

 Ungulates which have large eyes have the optic lobes or nates, 

 fig. 68, a, proportionally larger than they are in a Carnivorous 

 quadruped with a similar-sized brain. In both the ' testes,' ib. b, 

 are broader, but in Felis they also rise higher ; whilst in Un- 

 gulates, and especially Ruminants, the 6 nates ' show the greater 

 vertical developement. 1 In all Carnivores the ( testes' have a 



minor antero-posterior 

 extent than the ' nates.' 

 The white bands or 

 tracts ( f brachia ' in an- 

 thropotomy ), extending 

 along the outer sides 

 of the bigeminal bodies 



o 



to the thalami and com- 

 mencement of the optic 

 tracts, fig. 68, d, are 

 prominent in the higher 

 Quadrumana and in 

 Man. In most Gyren- 

 cephala the white fibres 

 continued from the optic lobes develope an oblong nodule, ib. e, 

 also containing grey matter (' corpus geniculatum ' of anthro- 

 potomy), which in the human brain is divided into an external 

 and internal portion. 



The f crura ccrebri ' formed by the pre- and post-pyramidal 



1 This difference I exemplified in the preparations, nos. 1326 A and 1826B, xx. 

 vol. iii. p. 30. 



Mcsenceplialon, upper view, Horse. 



