HUMAN AlfD MAMMALIAN. 3 



subsequent chapter. The oHvaries are connected with each other and with the 

 raphe by the arciform fibres, and are also united to the hypoglossal nuclei by bundles 

 of fibres, either directly or by the interposition of ceU nuclei. 



The antera-lateral nucleus {B) is now very prominent, from the number and size 

 of its cells. These are mostly stellate, sending their processes in all directions, the 

 group being traversed by the arciform fibres and by fibres derived from the central 

 gray substance, as well as by longitudinal fibres. This group is also united to the 

 caput, and in sections higher up to the remains of the cervix, by the cells formerly 

 scattered throughout the antero-lateral columns, but which are afterwards collected 

 into elongated groups (Fig. S*^). The restifortn (r, r) and post-pyramidal {p,p) 

 nuclei are now much increased in size, and are quite fiUed with cells of various 

 dimensions and forms, the ceUs of both nuclei reaching out into and soon entirely 

 filling the posterior and postero-lateral columns. 



As we ascend, the nuclei of the hypoglossal and spinal accessory nerves rapidly 

 increase in size and number of cells, the entire substance of the anterior or hypo- 

 glossal nucleus {H) being filled with large stellate cells, with the exception only of 

 that portion which forms on each side the lateral boundary of the central canal. 

 The posterior, spinal accessory or vagus nucleus (/S'), has also equally increased ; its 

 group of large, obovate cells is very conspicuous, the remainder of the nucleus 

 being entirely fiUed with smaller, scattered cells. The caput is mostly fiUed with 

 granules and smaller nuclei, with a few cells of medium size ; numerous cells being 

 scattered throughout the entire lateral and antero-lateral network. 



(3.) Still higher up (Plate I, Fig. 3 ; Plate XIII, Fig. 3") the central canal which 

 has been hitherto somewhat elongated, of a narrow oval form, changes to a trian- 

 gular shape with curved sides, the apex pointing forwards, and bridged behind by 

 a thick band of commissural fibres connecting the posterior nuclei, now the nuclei 

 of the vagus roots (Fig. S"", V). The principal changes to be noticed in this region 

 are the rapid increase in the number of cells forming the post-pyramidal (p, p) and 

 resti/orm (r, r) nuclei, which fill the entire posterior and postero-lateral columns, 

 encroaching on the caput and thick band of external arciform fibres, with both of 

 which they seem to be connected by numerous bundles of curving or wavy fibres 

 (Fig. 3", a). A remarkable collection of longitudinal fasciculi is here plainly mani- 

 fest, which, beginning a little lower down, comes now distinctly in sight just at 

 the entrance of the vagus roots (Z), separating them into anterior and posterior 

 divisions. The cells of the antero-lateral nucleus, instead of being collected into 

 compact groups as below, are somewhat scattered, forming various wavy groups 

 which nearly fill the antero-lateral columns of the medulla (B). 



(4.) As we continue to ascend (Plates I, XIII, Figs. 4, 4") the commissural bridge 

 between the two vagal nuclei' is split open, forming the fourth ventricle, on each 

 side of which are situated the nuclei of the hypoglossal and vagal nerves, the 

 anterior portion of the vagus nucleus being especially conspicuous from its crowd of 

 obovate cells. 



The longitudinal fasciculi in connection with the vagus nucleus are very promi- 

 nent, separating the roots into two divisions, the posterior bundles either entering 

 a small nucleus behind the longitudinal fasciculi, or bending around them towards 



