NERVOUS SYSTEM. VERTEBRATA. Ill 



differentiated. The mesial wall of the hemisphere is composed 

 of a large dorsal area the hippocampus, and a ventral spindle- 

 shaped area the tuberculum olfactorium (see fig. 31). A re- 

 latively narrow strip of thick ganglionic matter extending from 

 the lamina terminalis behind to the olfactory peduncle in front 

 separates these two areas ; this body may be called para- 

 terminal, because its most distinctive feature in the adult is 

 that it lies alongside the lamina terminalis, and in the foetal 

 brain is developed from those parts of the walls of the neural 

 tube which are placed alongside the end or terminal plate. Tts 



Fig. 30. 



- N EURO P. 



I- CORTEX. 





EPEND. 

 Section of pallium of Tropidonotus natrix, X 150. 



surface forms the precommissural area, and in Mammals its 

 upper part becomes stretched and otherwise modified to form 

 the septum lucidum (vide Journ. of Anat. & Phys. vol. xxxii. 

 p. 411). 



In Reptiles and Monotremes the peculiar cortex, of which the 

 tuberculum olfactorium is formed in Meta- and Eutherian 

 mammals, although present, is ill-defined ; so that the corpus 

 striatum seems to extend to the surface of the ventral half of 

 the brain. 



A comparison with the condition found in the Monotremes 

 (vide infra) and in the foetal state of all mammals, 'dearly 

 demonstrates that the whole of the mesial surface of the cerebral 

 hemisphere of the reptilian brain, which is not precommissural 

 area nor tuberculum olfactorium, represents and is homologous 



