138 ANATOMY OF VERTEBRATES. 



Each hemisphere is a bag of neurine folded or laid upon its 

 expanding stem, the hollow of the bag being the ventricle. This, 

 in the embryo, is capacious and simple, the wall being very thin. 

 It becomes thickened in different degrees at different places, most 

 so at the upper and outer sides. The wall, thus thickened, pro- 

 trudes at certain parts into the cavity, dividing and shaping it 

 into parts or recesses which Anthropotomy calls ( horns,' from their 

 curvature in Man. In lower Mammals the primitive cavity com- 

 monly retains more of the general shape of the hemisphere, and in 

 most Quadrumana, the lower more especially, the part accom- 

 panying the broad supracerebellar expansion of the hemisphere is 

 of corresponding capacity. The Orang, among Apes, still shows 

 the primitive character of this part of the ventricle : in the 

 Chimpanzee and Gorilla the growing walls reduce and begin 

 to shape it as a f horn,' showing also a beginning of a protu- 

 berance within it. In Archencephala the moulding of the ' pos- 

 terior horn ' is completed by the predominance of the internally 

 protruding wall ( : partie enroulee,' Leuret), to which, now, the 

 term ( hippocampus minor,' or ' pes hippocampi minor,' rightly 

 applies. 1 The fibres of the stem, augmented in number at each 

 accumulation of grey reuniting matter, diverge into and form 

 the main part of the wall in greatest proportion in the Lyen- 

 cepliala. 



The stem or ' crus ' is formed by the prepyramidal tracts, fig. 66, 

 ]), the olivary tracts f, the teretial and postpyramidal tracts, fig. 

 49, Y, and so much of the cerebellar tracts, fig. 66, t, as may not 

 have been expended in the formation of the ( nates,' b, ( testes,' n, 

 ( geniculate bodies,' y, and their common basis. Thus the crus 

 or stem of the hemisphere includes tracts of the myelon, connected 

 respectively with the sensory and motory roots of the nerves. 

 The part of the ' crus proseiicephali,' below or in front of the 

 ( locus niger,' consists of white fibres in a coarsely ( fasciculate ' 

 arrangement, fig. 123, d: the part above, derived from the tere- 

 tial, postpyramidal, and cerebellar tracts, is softer, with mixed 

 grey matter, and forms the f tegmentum,' ib. c. The fasciculate 

 fibres, after passing through and being reinforced by the grey 

 matter of the striated body, diverge in curves, fig. 66, c, fig. 122, s, 



1 The judicious and painstaking anatomist GRATIOLET seems to have foreseen some 

 late misconceptions of the nature of the hind part of the primitive ventricular cavity 

 in the Quadrumanous brain, in the following note : ' Toutefois, il ne peut etre 

 considere comme un signe A' elevation, car il est beaucoup plus grand en egard a la 

 partie enroulee du ventricule dans les singes, ou son developpement est enorme, que 

 dans I'homme, ou la partie enroulee 1'emporte evidemment sur lui. Cette remarque,' 

 he justly adds, ' est d'une haute importance.' XL", vol. ii. p. 75. 



