842 



COMPARATIVE ANATOMY 



As the brain grows in a bony case, it follows that as soon as the brain 

 has grown longitudinally the full length of this case, it must bend in the 

 various directions the case lays down for it. Therefore, in the mam- 

 mals, the posterior end of the hemispheres grow dorsally and downward, 

 and then forward again until that portion of the hemisphere which was 

 originally most posterior has now grown forward until it reaches, or at 

 least touches, the olfactory region. The part growing downward and then 

 forward grows over a part of the side-wall of the hemispheres which por- 



Corpus pineale (Epiphysis) 

 Commissura post. 



Commissura sup. 



Lamina chor. cpithcJialis ventr. Ill 



Stelle der Einstiilpung des 

 Plex. chorioideus 



Tela chor. ventr. IV 



Telencephalon 

 Diencephalon 



esencepha/on 

 Metencepha/on 



Corpus mamill 



Hypophysis Chiasma 

 Nn. optic. 



Hdhe des For. inter- 

 ventric. (Monroi) 



Commissura ant. 



Recessus optic. Lamina terminalis 



Fig. 471. 



7, Schematic median section of brain of a four month human foetus to show 

 the various changes caused by the developing hemisphere. (From Corning after 

 Burckhardt. ) 



II, Diagram of the development of the corpus callosum and septum pellucidum 

 in man. A shows the hemisphere in outline, ac, anterior commissure ; cc, corpus 

 callosum ; ep, epithelial roof of the third ventricle ; he, hippocampal commissure ; 

 It, lamina terminalis ; o, olfactory lobe ; oc, optic chiasma ; p, paraterminal body ; 

 s, septum pellucidum ; vh, vestigial precallosal and supracallosal hippocampus. 

 (From Kingsley after G. Elliott Smith.) 



