CEREBELLUM 177 



scription in chap. xx). This fascicukis extends forward and ventral- 

 ward from the cerebellum at the outer border of the gray in the lips 

 and floor of the isthmic sulcus, finally to reach the ventral commis- 

 sure, where some of its fibers decussate a short distance spinalward of 

 the fovea isthmi, mingled with those of the decussation of the f. re- 

 troflexus and spinalward of it. Its course as seen in horizontal sec- 

 tions is shown in figures 29-32 (f.teg.p.), and in sagittal sections in 

 figure 104 and previously published figures of the same specimen 

 ('36, figs. 19-21, trxb.teg.). 



Elective impregnations show that the brachium conjunctivum is 

 the largest component of this mixed fasciculus (figs. 71, 72). Many 

 of its fibers spread outward into the alba of the isthmic tegmentum 

 on the side of origin, and these include all the myelinated fibers of 

 the brachium. A residue of the unmyelinated fibers decussates in the 

 ventral commissure. Elective Golgi impregnations show that, at the 

 decussation, fibers of the brachium conjunctivum and tertiary vis- 

 ceral tract are mingled and that both enter a dense superficial neuro- 

 pil laterally of the crossing. Here the tertiary visceral fibers turn for- 

 ward in company with those of the secondary visceral tract to reach 

 the area ventrolateralis pedunculi, and the cerebellar fibers turn pos- 

 terodorsally and spread out in the alba of the isthmic tegmentum. 

 This primordial brachium conjunctivum may activate almost the en- 

 tire extent of the isthmic tegmentum diffusely on both sides. No evi- 

 dence has been found of a concentration of cells related with it which 

 could be regarded as a nucleus ruber. 



THE CEREBELLAR COMMISSURES 



In the body of the cerebellum there are two commissures, which 

 differ in position, connections, and functions. They are specifically 

 related with the two chief subdivisions of the cerebellar complex. 



The com. cerebelli (com.cb.) is a compact fascicle of well-myelinat- 

 ed fibers crossing more ventrally than the less myelinated com. vestib- 

 ulo-lateralis cerebelli (com.cb.i.), as shown in figures 10 and 91. It 

 crosses between the levels of figures 34 and 35. The com. cerebelli is 

 composed of fibers from two sources, which terminate chiefly in the 

 median body of the cerebellum. These are (1) fibers of the tr. spino- 

 cerebellaris (figs. 32, 33, 91) and (2) fibers of the sensory trigeminus 

 system. The latter are, in part, fibers of the ascending sensory V root 

 terminating in the cerebellum and, in part, axons of cells of the su- 



