THE BRAIN 703 



In a section of the cerebellar cortex three layers are to be dis- 

 tinguished, the most characteristic of which is the one in the 

 middle, in which occur the flask-shaped cells of Purkinje (see 

 Fig. 430). 



The apical dendrites of these cells ramify in the external layer, 

 while the efferent axon passes down internally into the central layer 

 of white matter. Afferent tendril fibres aborize round these cells. 



External to the Purkinje cell layer is the outer molecular layer, 

 which consists of irregular star-shaped cells, neuroglial cells, and the 

 dendrites of the Purkinje cells. The axon of the star-shaped cell 

 runs parallel to the layer for a certain distance, and then turns down 

 to arborize around the Purkinje cells. 



Internal to the Purkinje cell layer is the nuclear layer, or inner 

 molecular layer, therein afferent fibres the so-called moss fibres 

 arborize, forming curious mossy-like figures. In this layer are small 

 star-shaped cells, irregular cells of Golgi, and neuroglial cells. 



The underlying white matter is composed of the afferent axons 

 of the tendril and moss fibres, and the efferent processes of the Purkinje 

 cells. 



The cerebellum is connected to the brain-stem by three pairs of 

 peduncles: The inferior, or restiform body, to the medulla; the middle 

 to the pons ; the superior to the mid-brain. It is by these three sets 

 of channels that it receives messages from, and sends messages to, the 

 other parts of the central nervous system. The connections of the 

 cerebellum may *be tabulated as follows : 



Afferent Fibres to the Cerebellum. From spinal cord (1) By the 

 dorsal spino-cerebellar tract (direct cerebellar tract of Flechsig) to 

 the lower part of the vermis; (2) by the ventral spino-cerebellar 

 tract (antero-lateral ascending of Gowers) to the upper part of the 

 vermis by the superior peduncle. 



From the medulla by the inferior peduncle (1) To the vermis by 

 the internal arcuate fibres of the gracile and cuneate nuclei of the same 

 side; (2) to the vermis by the external arcuate fibres from the gracile 

 and cuneate nuclei of the opposite side; (3) to the vermis from the 

 inferior olive, chiefly of the opposite side; (4) to the vermis by fibres 

 from Deiters' nucleus, and directly from ganglia of the vestibular 

 nerve. 



From the pons to the lateral hemisphere by the terminal neurons 

 in the connection between cerebrum and cerebellum. These arise 

 from the nucleus pontis of the opposite side, around which the cortico- 

 pontine fibres terminate, and pass by way of the middle peduncle. 



From, the mid-brain, optic thalamus, and cerebral cortex, on the 

 opposite side by way of the superior peduncle. 



Efferent Fibres from the Cerebellum. Fibres gather from all parts 

 of the cerebellum to the roof and dentate nuclei and pass thence 

 (1) In the inferior peduncle to Deiters' nucleus, and thence to the 

 cord by the vestibulo-spinal tract; also upwards to the sixth and 

 third nerves, and downwards to the cord in the posterior longi- 



