The origin of the Corpus callosum, a contrib. upon the cerebral comni. etc. 543 



is increased by the fact that it is taken somewliat obliquely. The 

 frontal and temporal divisions of the anterior commissure are here 

 shown. 



Fig. 25. Transverse section of the brain of a pouch specimen, 4 cm long, 

 X 10. This brain is considerably more advanced than the former 

 and the section passes in front of the pillars of the fornix. The callosal 

 fibres as well as those of the anterior commissure extend well into 

 the dorsal portion of the mantle of the hemispheres. Here the pars 

 frontalis of the anterior commissure is distinct from the pars ol- 

 fac toria. 



Fig. 26 and 26«. This is through the inner mantle of the brain of a much 

 more advanced pouch specimen (75 cm) x 10. It is taken some di- 

 stance in fron t of the terminal plate in the region shown in the 

 plan, 26 a. It shows the character of the hii.pocampal sulcus and the 

 fibres of the slender callosal bundle passing upwards into the mantle. 



Fig. 27 and 27 a. This is a section of the same brain. The plan, 27 a, shows 

 that it passes through the transverse fissure and comprises the hippo- 

 campus and fimbria. The figure is designed to show that the rela- 

 tions of the posterior division of the corpus callosum are exactly 

 similar to those of the anterior division. 



Ovis. 



Fig. 28. This section is through the brain of an Embryo, 4.9 cm long. It shows 

 the condition of the commissures immediately after the fibres of the 

 corpus callosum have united in the centre. The anterior commissure 

 is a slender but compact bundle. It is widely separated from the cor- 

 pus callosum, which at this stage consists of fibres loosely uniting the 

 opposed hemispheral surfaces. The fibres cannot be distinctly follo- 

 wed around the hippocampal sulcus. The columnae fornicis are well 

 developed. 



