460 THE BRAIN OF MAMMALS, BY TH. MEYNEET. 



cessus cerebelli ad corpus quadrigeminum, which, erroneously, 

 as Arnold showed, has been given to the superior peduncle. 



Three kinds of medullary fasciculi interlace in the substance 

 of the valve. 1. The principal mass of its medullary portion 

 consists of the fasciculi of the frenulum. 2. With these prin- 

 cipal fasciculi are interwoven above the large decussating fas- 

 ciculi of the root of the fourth nerve (figs. 251, 4). 3. The 

 valve also includes longitudinal fasciculi from the superior 

 vermiform process which cross the middle line whilst still con- 

 tained in its substance, and near the posterior border of the 

 testes form a curve with the convexity upwards, in order to 

 run as the posterior fasciculi of the inferior lamina of the 

 fillet, in the back or posterior division of the pons to the spinal 

 cord. 



The latter fasciculi of the valve either occur as so frequent 

 an anomaly that Hirschfeld committed no great error in re- 

 garding them as the ordinary arrangement in his illustrations 

 of the structure of the brain, or we may consider that (vary- 

 ing considerably in their size) they are really normally present. 



As external prominence it will appear that none of the fas- 

 ciculi of the antero-lateral columns of the spinal cord proceed 

 directly from the cerebellum, though fibres do pass from it to 

 the posterior columns ; it follows that the innermost or most 

 posterior fasciculi of the deep-lying lamina of the fillet be- 

 longing to the valve, in all probability, likewise pass to these 

 latter columns of the cord. 



Were we however to regard this formation as a very com- 

 mon anomaly, such a variation of the origin of the posterior 

 columns from the cerebellum, in the form of an aberrant loop, 

 at some distance from the other fasciculi, would only constitute 

 an anomaly harmonizing with the general and essential type 

 of structure here met with, whilst even an exceptional passage 

 of fasciculi from the cerebellum into the antero-lateral columns 

 would constitute a real deviation from the type. The superior 

 peduncle, moreover, in its way to the cerebellum, is by no means 

 wholly unmingled with other fasciculi, as may be seen on 

 transverse section, being traversed at the level of origin of the 

 fifth pair by the portion of its large root proceeding from the 

 cerebellum (and in part covered by it, figs. 252 and 253, A' 5 d) ; 



