THE RHINENCEPHALON 



273 



forms part of the medial wall of the corresponding hemisphere (Fig. 182); and 

 the cavity, although sometimes called the fifth ventricle, develops as a cleft 

 within the lamina terminalis and, therefore, bears no relation to the true brain 

 ventricles, which are expansions of the original lumen of the neural tube (Fig. 

 165). 



The anterior commissure, like the hippocampal commissure, belongs to the 

 rhinencephalon. It is a rounded fascicle which crosses the median plane in the 

 dorsal part of the lamina terminalis just rostral to the columnae fornicus (Fig. 

 205). In a frontal section of the brain, like that represented in Fig. 187, it can 



Splenium of corpus callosum 

 Sulcus cinguli 



Parieto-occipital fissure 



Cuneus 

 Cakarine \ 

 fissure 



,/ // Body of corpus callosum 

 Body of form* / " Free potion of col. of fornix 



Septum pdlucidum 

 Intervent. foramen 

 Anterior commiss. 



Genu of 

 corpus 

 callosum 



Occipila 

 lobe 



Crus offornix 



Thalamus 



Fimbria of hippocampus 

 Dentate fascia of hippocampus 



Uncus 



Olfactory 



bulb 



Olfactory tract 

 Rostrum offorpus col. 

 , Rostral lamina 

 Optic nerve 



' 'Covered portion of column of 

 Mammillary body fornix 



Mammillothalamic tract 



Fig. 205. Dissection of the human cerebral hemisphere to show the fornix. Median view. 



(Sobotta-McMurrich.) 



be traced lateralward through the most ventral part of the lentiform nucleus. 

 It consists of two parts (Fig. 206). Of these, the more rostral is shaped like a 

 horseshoe and joins together the two olfactory bulbs. This part can be readily 

 dissected out in the sheep's brain (Fig. 199), but is poorly developed in man. The 

 remaining portion, and in man the chief component, joins the pyriform areas 

 of the two hemispheres together (Cajal, 1911). 



We are now sufficiently acquainted with the anatomy of the rhinencephalon 

 to undertake a study of the structure and connections of its various parts. 

 Because of the wealth of detail which this subject offers we must confine our at- 



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