512 



COMPARATIVE ANATOMY 



connexions of the cerebellum of fishes indicate that it is an important 

 correlating and coordinating center. (Fig. 41 iC) 



Amphibia, compared with fishes, have a degenerate cerebellum, this 

 reduction being correlated with a loss of physical activity. 



The cerebellum of reptiles differs only slightly from that of amphibia. 



In mammals, the cerebellum is much enlarged. Only its median 

 lobe or vermis corresponds to the cerebellum of lower vertebrates. The 



Dorsal 



Entrance median 



zone. septum. 



Median. . . ) Portion of 

 > dorsal 

 Lateral ) root. Dorsal root. 



Zona 

 ferminalis 



Zona 



spongiosa.' 



Substantia 

 gelatinosa. 



Pormatio (ti 

 reticularis. 



and 



Ventrn- media 

 Groups of nerve cells 



Central canal. 



Ventral root. White Ventral Ventral funiculus, 



commissure, median 

 fissure. 



Pig. 428. — Cross section of the Itimbar enlargement of the human spinal cord. X8. 

 (From Bremer's "Text Book of Histology.") 



two lateral lobes or hemispheres are mammalian novelties. Increase 

 of the cerebellar cortex by folding results in so complicated a structure 

 that the term arbor vitae applied to its white fiber tracts seems not inap- 

 propriate. Three paired bundles of fibers, the superior, middle and 

 inferior peduncles, connect it with adjacent parts of the brain. The 

 superior peduncles or brachia conjunctiva connect the cerebellum with 

 the midbrain; the middle peduncles or brachia pontis connect with the 

 pons: the inferior peduncles or restiform bodies connect with the medulla 



