14 Anatomy of the Nervous System 



(I). Running back from this on the ventral surface is a 

 narrow, white band, the olfactory tract (PI. II.). The ventral 

 part of the hemisphere, along which the olfactory tract runs, 

 is marked off by a longitudinal groove, the rhinal (or limbic) 

 fissure, which separates this region (the olfactory lobe) 

 laterally from the more dorsal parts of the hemisphere. The 

 gray matter subjacent and lateral to the olfactory tract 

 forms the lateral olfactory gyrus, which enlarges posteriorly 

 into the pyriform lobe, while the rounded gray mass medial 

 to the tract is usually known as the tuberculum olfactorium, 

 though it represents also the anterior perforated area (see 

 p. 91). The superficial part of the brain dorsal to the rhinal 

 fissure is entirely non-olfactory in its relations, and is known 

 as the neopallium. 



If the hemispheres be pressed apart so as to open up the 

 longitudinal cerebral fissure, a broad white band is seen con- 

 necting them. This is the corpus callosum. 



Projecting between the dorsal posterior poles of the 

 hemispheres and lying in the furrow between the superior 

 corpora quadrigemina, is the pineal body, a small gland 

 attached by a stalk to the unpaired part of the forebrain, 

 the diencephalon. The latter may be exposed by raising, or 

 better by cutting away the back parts of the hemispheres. 

 The stalk of the pineal body is attached to the extreme 

 posterior portion of the membranous roof of the cavity of 

 the diencephalon, the third ventricle. This roof, like that 

 of the fourth ventricle, contains a chorioid plexus, and must be 

 removed to expose the ventricle. The latter is almost com- 

 pletely obliterated by the fusion of its lateral walls over the 

 greater part of their area, forming the soft commissure or 

 intermediate mass. The dorsal part of the ventricle is bounded 

 at each side by a conspicuous longitudinal ridge, the habe- 

 nula, the posterior ends of the two habenulae being connected 

 by a thin curved band, the habenular commissure. Lateral 

 to this, the wall is extremely massive, containing the thalamus 



