THE CEREBELLUM. 



301 



duncles. The upper surface of the pons forms part of 

 the floor of the fourth ventricle. Its fibres are divided 

 into transverse and longitudinal. Of the former there 

 are two planes superficial and deep. The longitudinal 

 layers are likewise separated into two sets: the first 

 passes upward between the transverse planes; the deep 



FIG. 132. THE CEREBELLUM, UPPER SURFACE. 



set, above the deep transverse plane, forms part of the 

 fibres of the floor of the fourth ventricle. 



The cerebellum is situated below the posterior lobes 

 of the cerebrum. It is lodged in the inferior occipital 

 fossae. It weighs about five and one-half to six ounces. 

 It is about four inches transversely, two and one-half 

 inches antero-posteriorly, two inches vertically at the 

 thickest part. It is composed of a gray cortex and a 

 white medullary portion, in which there is imbedded an 



