NERVOUS SYSTEM 



161 



bral lobes. In the mammals as compared with other animals 

 the corpus callosum increases in thickness rather than in length. 



Let 



Pec 



Tl, 



Cba 



Tc 



pa 



Cca 



FIG. 82. Human brain viewed from beneath. P, Pons V. ; Tbo, Tractus opt. ; 

 Lpp, Grey lamina between Pons V. and corpora mam., Cca ; * In, Insula 

 cerebri : marginal elevations of deep cerebral stratum ; Tc, Tuber ciner. ; Tbo, 

 Tuber olfact. ; Let, Grey commissure; Ccl 2 and Pec. Parts of corp. call.; 

 Cba, White basal commissure ; Spa, Transverse gyrus consisting of white 

 substance interspersed %vith vascular orifices ; Cca, Corpora mamm. ; Gf, 

 Cerebral gyri ; T, Tegmentum of grey substance; B, Crus; Sr, Reticular 

 white substance of the temporal lobe ; Mo, Medulla obi. The Roman figures 

 represent the cerebral nerves. The hypophysis is absent. 



In proportion to the thickness of the human corpus callosum, 

 which corresponds to the greater height of the human brain, 



ii 



