PROTUBERANTIA ANNULARIS. 353 



SECT. III. PROTUBERANTIA ANNULARIS. 



The Annular Protuberance (Protuberantia Annularis, J\o- 

 dus Cerebri, Pons Varolii) is the large projecting body, placed 

 near the centre of the base of the encephaion, at the top of the 

 medulla oblongata, and upon the junction of the body of the 

 sphenoid bone with the basilar process of the os occipitis. ft 

 is convex, and about an inch in diameter, its transverse mea- 

 surement being a line or two larger than the other. It is di- 

 vided by a superficial fossa into two symmetrical halves, right 

 and left. 



When the pia mater is removed from the Protuberantia An- 

 nularis, the under surface of the latter is seen to be formed by 

 transverse medullary fibres which come from the crura cere- 

 belli. When these, which are commonly one or two lines in 

 depth, are removed by scraping or cutting, a cineritious mat- 

 ter is exposed, which is traversed by numerous layers of me- 

 dullary matter, also going in a transverse direction. About 

 two lines deep from the surface of the protuberance, near the 

 middle of each of its halves, are found some longitudinal me- 

 dullary fibres connected with cineritious matter, and which, 

 may be fairly traced as a continuation of the filamentous struc- 

 ture of the pyramidal bodies. These fasciculi, or filaments,, 

 passing on through the protuberance, are continued so as to 

 form the under surface of the crura of the cerebrum. 



Lying still deeper than the medullary fibres alluded to, there 

 is an accumulation of cineritious matter, intermixed with per- 

 pendicular medullary layers situated one behind the other. Be- 

 hind (or above when we stand erect) this intertexture, a small 

 fasciculus (the cord described by Rosenthal) of medullary mat- 

 ter exists, which is a continuation of the intermediate fascicu- 

 lus of the anterior medullary cord of the medulla spinalis, and> 

 may be traced afterwards to the superior face of the crus cere- 

 bri, where it terminates, as alleged by Rosenthal, in the Tu- 

 bercula Quadrigemina. 



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