94 



ANATOMY OF VERTEBRATES. 



middle lobe in anteroposterior extent, leaving an anterior or 

 6 semilunar ' fissure, and a narrower ( posterior notch,' ib. n, the 

 groups of lamellae bounding which are called, by some, ' post- 

 inferior lobes.' The hemispheres are commonly but not constantly 

 symmetrical ; both these and the middle lobe consist of numerous 

 lamellae, of white covered by grey neurine; the interlamellar 

 fissures are penetrated by folds of pia mater. The lamellae are 



65 



Upper surface of the cerebellum, and mesencephalon, Man. 



collected into groups, forming the ' lobes ' of the hemispheres, 

 which are divided by deeper fissures. The lamellae of the middle 

 or ' vermiform ' part are fewer, and more transverse or vertical 

 than those of the hemispheres ; they are also thicker, single ones 

 answering to, and connecting, two or more of the hemispheral 

 lamellae, fig. 65, v. 



A vertical section of either hemisphere, or of the median lobe, 

 displays a ramification of fibrous matter, the smaller or ultimate 

 branches of which are enveloped by laminae of grey matter. This 

 appearance suggested to the older Anthropotomists the name of 

 ' arbor vitae,' which it retains. The trunk of the tree is repre- 

 sented by a central nucleus of white matter, fig. 66, d, from the 

 upper and lower surfaces of which branch off, some at a right, 



