MAMMALIAN. 55 



polar cells of the outer network, through which a few small bundles may be traced 

 for a considerable distance, running around the inner border of the restiform body, 

 and sometimes apparently joining the anterior division of the auditory nerve. By 

 far the greater number, however, pass along the floor of the fourth ventricle, 

 occasionally turning off to join the oval cells near which they pass, until the anterior 

 border of the nucleus is nearly reached, in the neighborhood of the fasciculus teres 

 (Plate XVI, Fig. 44). Here they turn off in every direction, joining numerous 

 bundles derived from the cerebellum, as well as those derived from the anterior 

 division of the root, with which they pass across the root of the facial or interlace 

 with its fibres, forming the very beautiful fringe so often spoken of and which may 

 be seen very distinctly in Plate XVI, Figs. 44 and 12". These fibres pass into the 

 antero-lateral network between the facial roots and the raphe, some of them probably 

 entering the numerous small cells found in this locality ; others may be traced 

 across the abducens roots, interlacing with some of their fibres and then passing 

 onward towards the raphe, where some of these bundles are plainly seen to decus- 

 sate with those derived from the opposite side. 



With regard to the anterior division of the root, Clarke states that it " consists 

 of two portions : the principal portion penetrates the meduUa beneath the restiform 

 body, and nuuiing along the outer side of the caput cornu, enters both parts of the 

 auditory nucleus ; the other portion runs backward along the upper border of the 

 restiform body, which it accompanies over the superior peduncle to the inferior 

 vermiform process of the cerebellum."^ To this account, with which my own obser- 

 vations entirely agree, I shall add a few details. The a7iterior division of the audi- 

 tory penetrates the arciform plexus in a broad, compact mass of fibres, which soon 

 spread out somewhat, being separated by intervening longitudinal fibres into 

 numerous smaller bundles. A portion of these turn off shortly after passing 

 through the arciform plexus, and joining the posterior division of the root wind 

 round the outside of the restiform body, in which course they are constantly joined 

 and reinforced by other fibres, often very numerous, derived from the restiform 

 body itself (Figs. 9% 10", 12") ; sometimes these fibres instead of turning off and 

 winding round the outer border of the restiform body, pass directly through its 

 substance (Fig. 10"). Their ultimate destination cannot be distinguished from that 

 of the fibres belonging to the posterior division of the root which they accompany. 

 These fibres not unfrequently penetrate the restiform body to so great an extent 

 that the latter nearly disappears, seeming almost hidden beneath the network of 

 transverse fibres (Plates III and IV, Figs. 1, 2, 13, and Plate IX, Figs. 35, 36). 



The principal portion of the anterior division of the root is subdivided into a 

 considerable number of smaller bundles, which pass behiiad the caput cornu separat- 

 ing it from the restiform body, and enter both portions of the nucleus, just at the 

 apex, where the anterior portion of the nucleus is prolonged laterally to join as it 

 were, the outer network. Through the apex the fibres pass onward, spreading out 

 into an almost inextricable network, crossing at different angles the fibres derived 

 from the restiform body and from the cerebellum. 



• Proceedings of the Royal Society, June 20, 1861. 



