NERVOUS SYSTEM. VERTEBRATA. 113 



Tn the thalamencephalon the tracts and nuclei are larger and 

 more numerous than in lower forms, indicating a greater com- 

 plexity of connection between the fore and hind parts of the 

 brain, due mainly to the presence of cortical tracts. The 

 nuclei rotundi, in which the main part of the strio-thalamic 

 tracts terminate, are particularly large and form the greater 

 part of the protuberant thalami. There are also two end nuclei 

 of some of the optic fibres which are supposed to represent the 

 lateral geniculate bodies. On the other hand, the connection 

 between the hypothalamus and cerebellum is usually very weak. 

 The fasciculus longitudinalis posterior rises partly from the 

 hypothalamus, but mainly from a large-celled nucleus in the 

 floor of the mid-brain. 



The epiphysis is in most cases strongly developed, and in 

 Lacertilia is in connection by its distal end with a median 

 vestigial eye lodged in a foramen in the cranial roof. 



The infundibulum shows scarcely any signs of a saccus vas- 

 culosus except in the swimming forms. The cerebellum, as in 

 Amphibia, owing to the small size of the tracts that enter it, 

 has no clearly defined inner fibrous layer. In the Reptiles there 

 is an increase in the number of acoustic nuclei, corresponding 

 to the development of a rudimentary cochlea (lagena). 



LACERTILIA. 



D. 127. The brain of a Monitor Lizard ( Varanus varius). 



In general form this is a typical example of the brain of 

 a Reptile. The olfactory bulbs are long and narrow, and are 

 united by short peduncles to the pear-shaped hemispheres. 

 The hemispheres form the broadest part of the brain, and 

 parts of them, representing the pyrif orm lobes, bulge down- 

 ward behind the tuberculum olfactorium to form pseudo- 

 temporal lobes. Posteriorly they are contiguous with the 

 anterior face of the optic lobes and completely cover the 

 thalamencephalon. In the dorsal mid-line, between the 

 cerebrum aud optic lobes lies the club-shaped epiphysis, 

 with a small vestigial eye in connection with its distal end. 

 The optic lobes are well developed, and form a pair of 

 rounded eminences separated from one another in the mid- 

 line by a deep furrow. 



VOL. II. I 



