THE HINDBRAIN 



357 



ib) 



(c) 



The various folds of the cerebellar surface are designated 

 as indicated in Figs. 118 and 119. The parts named lobulus 

 ansiformis and lobulus paramedianus together make up the 

 cerebellar hemisphere. 



The cerebellum is concerned chiefly 

 with the co-ordination of muscular action, 

 the regulation of the "tone" of the 

 muscles, and the preservation of the 

 equilibrium of the body. The cerebellar 

 hemispheres are specially related to the 

 cerebral hemispheres and receive large 

 numbers of fibres (from the pons) 

 bearing impulses from the latter so 

 that they may co-ordinate the con- 

 tractions of muscles activated by direct 

 impulses from the same source. 



The areas of the two crura of the 

 ansiform lobule indicated by hatching 

 in Fig, 120 have been shown to be 

 proportional to the weight of the muscle 

 masses of the fore and hind limbs 

 respectively in the rabbit and the re- 

 mainder of the hemisphere appears to be related to ability 

 to perform quick, powerful movements of the hind limbs 

 and trunk. 



The anterior medullary velum (velum medullare anterius) 

 is the thin membrane underlying the anterior portion of 

 the cerebellum, attached to the ventral surface of the latter 

 and connecting it w4th the inferior colliculi (Fig. 124). It 

 forms a small anterior portion of the roof of the fourth 

 ventricle. 



The fourth cranial, or trochlear nerve (n. trochlearis), 

 which supplies the superior oblique muscle of the eye, 

 emerges from the anterior medullary velum and runs 

 transversely on to the lateral surface of the cerebral 

 peduncle. Here the cut end of the proximal portion of the 

 nerve is usually to be found. 



Fig. 120. Lat- 

 eral view of the 

 ansiform lobule 

 as in Fig. 118, 

 the superior 

 crus hatched 

 t r aiis-verse ly 

 and the inferior 

 crus hatched 

 vertically. The 

 areas of the two 

 crura are pro- 

 portional to the 

 weights of the 

 muscles of the 

 anterior and 

 posterior limbs 

 respectively, in- 

 dicating a prob- 

 able functional 

 relation to these 

 muscles. 



