THE CEREBELLUM. 



239 



nucleus. In mammals the direct cerebellar tract, which is the 

 secondary visceral sensory tract from the spinal cord, runs lateral 

 to the somatic sensory tracts and both are included in the corpus 

 restijorme. The anterior brachium, brachium conjunctivum, in 

 lower vertebrates (Figs. 112, 117) runs from the lateral lobe partly 

 through and partly beneath the secondary gustatory nucleus and 

 passes diagonally downward and forward to the base of the mes- 

 encephalon. In mammals (Fig. 126) it is enormously larger and 

 has made room for itself by shifting other structures to one 

 side. In all vertebrates the anterior and posterior brachia cross 

 one another as they enter the cerebellum like the two limbs of a 

 letter X, the anterior brachium passing mesially to the posterior. 

 In mammals a third brachium is added, the brachium pontis, 

 which goes vertically downward between the diverging anterior 

 and posterior brachia. 



STRUCTURE OF THE CEREBELLAR CORTEX. The most con- 

 spicuous elements in the cerebellum are the Purkinje cells. These 

 differ from those in lower vertebrates chiefly in the mode and 

 regularity of their arrangement. The cell-bodies are situated 

 between the molecular and granular layers and the dendrites 

 spread in the molecular layer. The arrangement is such that 

 in any fold of the cerebellum the dendrites of each Purkinje cell 

 spread like a fan across the fold (Fig. 121). The dendrites are 

 provided with small lateral spines. From the deeper end of the 

 cell-body arises the neurite which penetrates the white layer. In 

 the first part of its course it gives off several collateral branches 

 which rise toward the surface and end in the granular or molecular 

 layer. The neurites then become myelinated and proceed as 

 constituent fibers of the white fiber layer. 



The granular layer contains both granule cells and cells of 

 Golgi's type II. The granule cells are very numerous and closely 

 packed together and, like those of lower vertebrates, have short 

 dendrites which end in claw-like tufts of small branches. The 

 neurites are exceedingly fine, rise directly into the molecular layer 

 and divide in T T form into two branches which run parallel with 

 the surface of the folds of the cortex. Among these fine fibers 

 of the molecular layer are imbedded the dendrites of the furkinje 



