MAMMALIAN. 47 



the back of the nucleus, crossed by bundles coming down from the cerebellum 

 towards the apex of the nucleus. 



(6.) In Plate XVI, Fig. 12'', the projection formed on the posterior auditory root, 

 as it emerges from the meduUa, is still conspicuous, but the fibres of the root have 

 very much diminished in number. The ganghonic enlargement consists partly of 

 numerous longitudinal or oblique fibres, intermixed with others running in a trans- 

 verse direction ; the latter, which are derived from the posterior parts of the medulla, 

 cross the fibres of both divisions of the auditory root and pass onward as part of the 

 external band of arciform fibres so conspicuous throughout the trapezium. As we 

 ascend, the projection still continues to be conspicuous (Plate IV, Fig. 13), but the 

 posterior root-bundles continually diminish in number and presently disappear. 

 The prominence is fiUed Avith numberless very small cells, round and obovate, meas- 

 uring about 2 Jg^ to -j^- of an inch in diameter. In sections still higher up the 

 cells diminish in size, the prominence appearing more and more like an e:itension 

 of one of the cerebellar folds filled with small cells and granular nuclei. 



In the cat the group of cells placed on the back of the auditory root forms a very 

 conspicuous prominence, seen in Plate IX, Fig. 35, as a dark mass lying along the 

 roots, and separated by a deep sulcus from the flocculus. The cells become more 

 and more numerous as we ascend, and are often found intermingled with the roots 

 themselves. After the level of the facial roots is attained (Fig. 36), the mass is 

 brought into close contact with the folds of the flocculus, and the cells are seen tt.> 

 be evidently qf a similar nature to those found in the convolutions of the cerebellum, 

 only in a somewhat denser and larger mass. The structure of the caput in this 

 region is somewhat peculiar. Instead of consisting of a loose fibrous mass contain- 

 ing scattered cells, as is the case in the lower regions of the medulla, it is here 

 divided into several i^unded masses, five or six in number, closely crowded with 

 cells of moderate size, very much resembling the appearance of those masses in 

 the lower part of the trapezium which were shown to be the commencement of the 

 upper olivary bodies. The caput is very early brought into connection with the 

 anterior part of the auditory nucleus by several rather thick bundles of fibres, and 

 its whole substance appears to be closely connected with both portions of the audi- 

 tory nucleus. 



(7.) As we ascend, the restiform columns are continually encroached upon more 

 and more by fibres radiating from both roots of the auditory, which penetrate and 

 almost conceal them (Plate IV, Fig. 13). They are, at the same time, pushed 

 backwards together with the auditory nucleus, by the formation and enlargement 

 of the nucleus of the abducens and facial, and by the contraction of the lateral 

 boundaries of the fourth ventricle, until, as Clarke^ and Stilling^ have both shown, 

 they are ultimately thro-wn backwards into the cerebellum, together with the pos- 

 terior portion of the auditory nucleus. 



The anterior root of the auditory seems to consist, in the upper part of the trape- 

 zium, of two quite distinct divisions (Figs. 12, 12", 13); a compact bundle proceed- 



* Proceedings of the Royal Society, June, 1861. 

 " Pons Varolii. 



