THE PONS 



659 



THE PONS 

 The pons (Varolii) is that part of the brain stem which Ues between the medulla 

 and the cerebral peduncles; it is marked off from these ventrally by anterior and 





Fig. 502. — Cross -8Ecno>f of Mkdull.v Oblont,.\ta of Horsk. P.\ssino through F.\ci.\l Nlclf.us. 

 CV, Corpus restifonne; T). ilorsal longitudinal fasciculus; I'a, ascending part of facial nerve; L, fillet; 

 A'7, nucleus of facial nerve; NS, triangular nucleus of vestibular root of eighth nerve; \8' , spinal root of eighth 

 nerve; P(/, pyramid; Ra, raphe; li7 , radicular part of facial nerve; RS, vestibular root of eighth nerve; &g, 

 .substantia gelatinosa; Ta, posterior end of tuberculuin acusticuni; l', spinal root of trigeminus. (Ellenberger- 

 Baum, Anat. d. Ilaustiere.) 



posterior grooves. Viewed from below it is elongated transversely, convex in both 

 directions, and presents a wide shallow median groove (Sulcus basilaris), which 



f/ \ 



Fig. 503 — Cross-section of Medull.a. Oblongata of Horse; Section Passes through Middle of Corpus 



Tr.\pezoideu.m. 

 Cr, Corpus restiforme; Z>, dorsal longitudinal bundle; Fa, ascending part of facial nerve; Fa' , emergent or 

 descending part of facial nerve; R7 , root of facial nerve; L, fillet; .1/, central white matter of cerebellum; NB,. 

 abducens nucleus; 'NS, triangular nucleus; KS' , nucleus of Deiters; A'S", tuberculum acusticura; Oo, anterior 

 olive; Py, pyramid; R6, root of abducens nerve; R7 , root of facial nerve; Re, cochlear nerve; Rv, vestibular nerve; 

 iS'.(7, substantia gelatinosa; T, corpus trapezoideum; T', spinal root of trigeminus. (Ellenberger-Baum, Anat. d. 

 Haustiere.) 



lodges the basilar artery. Laterally a large part of its mass curves upward and 

 backward into the base of the cerebellum, forming the middle cerebellar peduncle 

 (Brachium pontis). The superficial origin of the trigeminal (fifth) nerve is at the 



