104 ANATOMY OF THE CENTRAL NEETOUS SYSTEM. 



anterior (external) lodges principally the dendrites from the posterior 

 lamina. 



Just at the boundary of the two laminae lies a layer of large cells extra- 

 ordinarily similar in all vertebrates, — the layer of Cells of Purkinje, and 

 partly in the posterior or internal cerebellar lamina (granular layer). 



The small multipolar ganglion-cells which fill the internal lamina 

 seem all to send up their neuraxons into the molecular or external lamina. 



There are, however, in this layer, and close to the cells of Purkinje, 

 several other types of cells which, though known in birds and fishes, have 

 been closely studied in mammals, and will, therefore, be described later. 



The mass of fibers which pass into the cerebellum in amphibians and 

 reptiles is so small that they scarcely make a separate layer on the epithelium 

 of the ventricle, but break up at once and pass into the fine net-work of the 

 latter. In teleosts, selachians, and higher vertebrates the condition is differ- 



Fig. 57. — Somewhat diagrammatic sagittal sections tlirough: (J-) Cerebel- 

 lum of a lizard; (B) Type of cerebellum of an alligator, crocodile, or turtle; (C) 

 Type of cerebellum of a bird or mammal. To illustrate the increase of the cere- 

 bellum through folding of the cerebellar plate in the direction of the arrow 

 over A. 



ent. Here such a mass of medullated fibers pass into the cerebellum that 

 one may always observe, between the epithelium of the ventricle and the 

 internal or posterior lamina, a separate and sometimes very important layer 

 composed solely of these afferent fibers. This is the medullary layer, or 

 center of the cerebellum. The figure of Vara7itis (Fig. 56) shows the 

 medullary center only in traces. Into this layer pass tracts from the mid- 

 brain and the thalamus, which are highly developed in fishes, but which 

 are also demonstrable in other animals. For the lower vertebrates the 

 material is, at present, insufficient. "What is known, however (Teleosts, 

 Schaper; Birds, E. y Cajal, Kolliker, and Edinger), shows that even in 

 the more detailed relations the lower vertebrates are similar to the mammals. 

 It may be thus briefly summarized: In the cerebellum fibers end and 



