186 Anatomy of thi; Rabbit. 



tentorium cerebelli. These parts contain the superior sagittal and 

 transverse venous sinuses. 



On the ventral surface of the brain as removed appear the basilar 

 and internal carotid arteries and their branches. These vessels should 

 be kept intact for examination at a later stage. 



For the primary divisions of the brain see p. 34. 



4. The superficial features may be identified as follows: 



IN THE PROSENCEPHALON: 



(a) The greatly enlarged cerebral hemisphere (hemisphaerium 

 cerebri) forms with its fellow of the opposite side the largest 

 portion of the brain. The two structures are separated by the 

 longitudinal cerebral fissure, but are connected with one 

 another by the commissures indicated below. 



(b) The olfactory bulb (bulbus olfactorius) is a small expansion 

 lying at the anterior end of each hemisphere. Its cut end 

 represents the point of origin of the first cranial or olfactory 

 nerve, the various divisions of which may be found on the 

 skull, where they may be traced into the perforations of the 

 cribriform plate. 



(c) The olfactory bulb is the anterior portion of the olfactory 

 lobe, or olfactory brain. When traced backward on the 

 ventral surface of the brain it is seen to be replaced by a 

 white band of fibres, the latter forming the olfactory tract 

 (tractus olfactorius). The tract ends posteriorly in an 

 expanded portion of the brain, which, from its shape, is 

 described as the lobus piriformis. The olfactory brain as 

 thus deiined is separated superficially from the remaining 

 portions of the cerebral hemisphere by a longitudinal furrow, 

 the limbic fissure (fissura limbica), which passes along its 

 lateral margin. The anterior portion of the furrow, known 

 as the anterior rhinal fissure, separates the olfactory tract 

 laterally from the narrow anterior" portion of the cerebral 

 hemisphere. The corresponding posterior portion of the fur- 

 row, the posterior rhinal fissure, separates the lobus piriformis 

 from the posterior enlarged portion of the hemisphere. The 

 slight angle formed at the junction of the anterior and 

 posterior rhinal fissures is the point of origin of a faint 

 depression extending upward on the cerebral hemisphere. 

 It represents a rudimentary, lateral cerebral (Sylvian) fissure. 



(d) The corpus callosum is a broad white commissural band 

 passing transversely from one hemisphere to the other. Its 

 median portion may be exposed by pressing apart the 

 medial margins of the hemispheres at the longitudinal 

 cerebral fissure. 



(e) The pineal body (corpus pineale) is a small somewhat 

 conical structure lying between the dorsal posterior tips of 

 the cerebral hemispheres, and connected by a hollow stalk 



