136 



ANATOMY OF VERTEBRATES. 



speedily followed by the ( postsylvian ' 9. A more or less inter- 

 rupted fissure divides lengthwise the sylvian or supersylvian fold, 

 ib. (j, from the median, /, and medilateral, m, tracts. The lamb- 

 doidal fissure, 13, extends toward the outer part of the hemisphere : 

 the pre-coronal tract of brain is fissured into subdivisions, chiefly 

 longitudinal : the foetal brain, at seven months, figs. 113,116, resem- 

 bles, in superficial cerebral marking, that of the latisternal apes, ib., 

 Chimpanzee, but is broader anteriorly, deeper and longer behind. 



In the foregoing summary we have seen that the fissures which 

 break the surface of the mammalian brain are of different kinds, 

 degrees, and values. Some, in the course of development and 

 elevation of the primary masses, divide one from the other ; as 

 the cerebrum from the optic and olfactory lobes, the cerebrum 

 from the cerebellum, and this from the macromyelon. Some 

 subdivide primary masses into symmetrical halves, as e.g., the 

 inter-hemispheral fissure, the inter-olfactory fissure, and the shal- 

 lower indent between the mammalian optic lobes or ' nates.' 

 One or two fissures of the cerebrum make folds that project into 

 the hemispheral cavity or ventricle, e. g. the hippocampal and, in 

 Man, the posthippocampal : most are confined to its crust or wall, 

 and of these, as I showed in 1833, some, from their relative con- 

 stancy, depth, and symmetry, may be termed s primary,' while 

 others are of ' secondary ' or inferior rank. 



The following are those which are noted by figures in the illus- 

 trations of the present work :— 



Cerebral Fissures, in the order mainly of their constancy in the Mammalia. 



The following are the cerebral folds which are indicated by 

 letters in the illustrations of the present work, with the synonyms 

 of original labourers in this field of anatomy : — 



