294 ANATOMY OF VERTEBRATES. 



primary divisions of the brain,, but retain the form and character 

 of simple smooth nodules. Each lobe has its ventricle, fig. 191, 

 r, containing a ' corpus striatum,' fig. 193, i, in which 

 the ' crus cerebri,' fig. 194, i, principally expands ; also a 

 smaller oblong eminence connected with the e thalami optici,' 

 fig. 193, 2; and a transverse body extending anteriorly to the 

 mesencephalon from the base of one lateral ventricle to the 

 other. The choroid plexus is shown in the left ventricle of 

 fig. 193. The olfactory lobes, of a pyramidal form, have their 

 base defined by a fissure from the hemispheres ; each has 

 its ventricle, fig. 191, k, which communicates with the 'lateral' 



one, r. 



The myelonal canal, fig. 191, g, is continued along all the 

 encephalic masses, in which it expands, and assumes the name 

 of 'ventricles,' the narrower intercommunicating canal being 

 the 'iter.' The 'fourth' or epencephalic ventricle is single : the 

 hypoarian ventricles, in fishes, form a pair ; as do, likewise, 

 the mesencephalic, prosencephalic, and rhinencephalic ventricles. 

 The ' iter ' or common passage between the ep- mes- and pros- 

 encephalic ventricles, includes the cavity called ( third ventricle ' 

 in Anthropotomy : to which cavity the mesencephalic ven- 

 tricles are reduced by the consolidation of the optic lobes in 



Mammals. l 



The epencephalic or 'fourth ' ventricle, exposed in figs. 193, and 

 194, c, shows the 'teretial' columns bounding the 'calamus' or 

 median fissure : external to these are ( funicular ' and ' pre- 

 pyramidal tracts : the restiform columns, forming the sides and, 

 anteriorly, the roof of the ventricle show grey and white striae 

 on their inner surface ; the cerebellum is removed from their 

 anterior union at s, fig. 194. The mesencephalic base which 



1 The influence of the nomenclature of human anatomy, reflected downward upon 

 the dawning structures of the lower animals which culminate in Man, is nowhere more 

 obstructive to a plain and true indication of the nature of parts than in regard to those 

 of the brain. The ventricles, for example, were indicated by numbers, or by position. 

 But four of the primary ventricles, viz., the mesencephalic or optic pair, and the 

 rhinencephalic or olfactory pair, which are present in the majority of vertebrates, are 

 obliterated in Man ; whilst the interspace of commissural lamelke, exceptionally deve- 

 loped in the complex cerebrum of Man, and some higher Mammals, is made a 'fifth 

 ventricle,' as if it were a structure of correlative significance and importance with the 

 ventricles properly so called. Those cavities moreover in the human prosencephalon 

 are specialized as ' lateral, ' being the only ventricles retaining the parial state which 

 is shown by the mcs- ancl rhin-encephalic ventricles in all oviparous Vertebrates. 

 Whoever will carry out the application of neat substantive names to the homologous 

 parts and structures of the encephalon, as they may be ascensively determined, will 

 perform a good work in true Anatomy. 



