158 



THE NERVOUS SYSTEM. 



Transverse section 



through tlie hinder 

 portion of the cere- 

 bral hemispheres ; 

 from Stieda. 

 f Lateral ventricle. 

 c' Coninuin ventricle 



of Stieda. 

 d Longitudinal fibres. 

 / Anterior prolonga- 

 tion of the third 

 ventricle. 



a common cavity [Ventricidus coitninum lohorum heniisjjJiaericoriim, 

 Stieda). 



In g"eneral terms, eacli ventricle may be said to be a semilunar 

 cavity, prolong-ed backwards and forwards (Fig-. 107 c); the outer 

 wall is always more or less concave, while the 

 inner varies according- to the part of the hemi- 

 sphere examined. At the anterior and j^osterior 

 extremities the inner wall is convex and bulg-es 

 into the cavity (Fig". 107) ; in the middle portion 

 of the cavity the inner wall presents a longi- 

 tudinal groove ( Veutrlcidl lateralis cormi inter- 

 num, Reissner), (Fig. 108 ^/), and consequently 

 the inner wall has here two rounded masses, an 

 upper and a lower {Corjms striatum^ Wiedersheim), 

 projecting into it. By tracing them backwards 

 and forwards, the lower swelling is seen to in- 

 crease at the expense of the upper, while at the 

 same time the lateral grooves disapj^ear; the 

 outline of the cavity shown in Fig. 107 is then 

 obtained. The roof of the ventricle is arched and broader than 

 the floor, which, in the middle part, exists only as a vertical slit 

 (Fig. 108), [Ventriculi lateralis cornu ivferius, Reissner): towards 

 the anterior and posterior extremities it widens and becomes 

 shallower (Fig. 107). 



The cerebral hemispheres and olfactory lobes 

 are composed of a fine granular matrix, enclosing- 

 spindle-shaped, rounded, or pear-shajîed nerve 

 cells and nuclei, and containing very fine fibres. 

 The cells (Fig. 109 li) are more numerous towards 

 the ventricle, and somewhat sparse towards the 

 superficial sm'face. The cells are of two chief 

 sizes, the smaller and more numerous average 

 0*004 nim. to O'OoS mm. in diameter ; they are 

 found chiefly in the deeper portions of the 

 section, but also form a very thin irregular 

 layer beneath the pia mater : the larg'er cells have an average 

 diameter of o'oio mm. to 0"0i2 mm., and are placed towards 

 the periphery, especially in the dorsal part of the inner wall. 



In this irregular collection of cells the following centres have 

 been described : (i) Tlie nucleus, through which the corjms callosum 

 passes (Koppen) ; (2) tlie lower internal or me<lian cell-area 



Transverse section near 

 the middle of the cere- 

 bral hemispheres. 



c Lateral ventricle. 



d Groove on the inner 

 wall. 



