THE HIND-BRAIN OR RHOMBENCEPHALON 793 



lentate nucleus of the cerebellum and emerge from the hilus of this nucleus; 

 a few arise from the cells of the smaller gray nuclei in the cerebellar white sub- 

 stance, and others from the cells of the cerebellar cortex. They are continued 

 upward beneath the corpora quadrigemina, and the fibers of the two peduncles under- 

 go a complete decussation ventral to the Sylvian aqueduct. Having crossed the 

 middle line they divide into ascending and descending groups of fibers, the former 

 ending in the red nucleus, the thalamus, and the nucleus of the oculomotor nerve, 

 while the descending fibers can be traced as far as the dorsal part of the pons; 

 Cajal believes them to be continued into the anterior funiculus of the medulla 

 spinalis. 



As already stated (page 762), the majority of the fibers of the ventral spino- 

 cerebellar fasciculus of the medulla spinalis pass to the cerebellum, which they 

 reach by way of the superior peduncle. 



The middle cerebellar peduncles (brachia pontis) (Fig. 705) are composed entirely of 

 centripetal fibers, which arise from the cells of the nuclei pontis of the opposite side 

 and end in the cerebellar cortex; the fibers are arranged in three fasciculi, superior, 

 inferior, and deep. The superior fasciculus, the most superficial, is derived from 

 the upper transverse fibers of the pons; it is directed backward and lateralward 

 superficial to the other two fasciculi, and is distributed mainly to the lobules on 

 the inferior surface of the cerebellar hemisphere and to the parts of the superior 

 surface adjoining the posterior and lateral margins. The inferior fasciculus is 

 formed by the lowest transverse fibers of the pons; it passes under cover of the 

 superior fasciculus and is continued downward and backward more or less parallel 

 with it, to be distributed to the folia on the under surface close to the vermis. 



The deep fasciculus comprises most of the deep transverse fibers of the pons. 

 It is at first covered by the superior and inferior fasciculi, but crosses obliquely 

 and appears on the medial side of the superior, from which it receives a bundle; 

 its fibers spread out and pass to the tipper anterior cerebellar folia. The fibers 

 of this fasciculus cover those of the restiform body. 1 



The inferior cerebellar peduncles (restiform bodies) pass at first upward and lateral- 

 ward, forming part of the lateral walls of the fourth ventricle, and then bend 

 abruptly backward to enter the cerebellum between the superior and middle 

 peduncles. Each contains the following fasciculi: (1) the dorsal spinocerebellar 

 fasciculus of the medulla spinalis, which ends mainly in the superior vermis; (2) 

 fibers from the gracile and cuneate nuclei of the same and of the opposite sides; 

 (3) fibers from the opposite olivary nuclei; (4) crossed and uncrossed fibers from the 

 reticular formation of the medulla oblongata; (5) vestibular fibers, derived partly 

 from the vestibular division of the acoustic nerve and partly from the nuclei in 

 which this division ends these fibers occupy the medial segment of the inferior 

 peduncle and divide into ascending and descending groups of fibers, the ascending 

 fibers partly end in the roof nucleus of the opposite side of the cerebellum ; (6) 

 cerebellobulbar fibers which come from the opposite roof nucleus and probably 

 from the dentate nucleus, and are said to end in the nucleus of Deiters and in the 

 formatio reticularis of the medulla oblongata; (7) some fibers from the ventral 

 spinocerebellar fasciculus are said to join the dorsal spinocerebellar fasciculus. 



The anterior medullary velum (velum medullare anterius; valve of Vieussens; superior 

 medullary velum) is a thin, transparent lamina of white substance, which stretches 

 between the superior peduncle; on the dorsal surface of its lower half the folia 

 and lingula are prolonged. It forms, together with the superior peduncle, the 

 roof of the upper part of the fourth ventricle ; it is narrow above, where it passes 

 beneath the inferior colliculi, and broader below, where it is continuous with the 

 white substance of the superior vermis. A slightly elevated ridge, the frsenulum 



1 See article by E. B. Jamieson, Journal of Anatomy and Physiology, vol. xliv. 



