4 GRAY SrBSTANCE OF THE MEDULLA OBLONGATA. 



the anterior part of the nucleus. The resiifoii'tn and post-pyramidal nuclei are 

 filled with numerous cells, and the latter is closely connected with the vagus nucleus 

 by means of a spur from each, the post-pyramidal body being as it were wedged or 

 dove-tailed into the vagus nucleus. The cells of the caput gradually increase in 

 size and number as we ascend, the caput itself being traversed by the vagus roots. 

 The longitudinal fasciculi in connection with the vagus continually increase in 

 size, and are reinforced by another system of bundles (m) which appear in that 

 portion of the nucleus from which the auditory nucleus is subsequently developed. 

 The lower part of the raphe constituting the olivary commissure contains many 

 cells, rather larger than those of the olivary bodies, and scattered cells are found 

 throughout the entire length of the raphe, as well as in aU parts of the anterior 

 and antero-lateral network. At about this height little nuclei are found con- 

 necting the raphe and hypoglossal nuclei with the olivary bodies and antero- 

 lateral nuclei. 



(5.) StUl higher up (Plates I, XIII, 6, 6") the hypoglossal nucleus begins to 

 diminish somewhat in size, its cells being smaller and much less numerous," though 

 a considerable number of large cells are still to be seen as long as the nucleus con- 

 tinues distinct. The cells of the vagus nucleus are very numerous and the roots very 

 distinct. 



Posteriorly we begia to trace the formation of a new nucleus {A), in the hmder 

 portion of the vagus, or rather between the vagal and post-pyramidal nuclei. This 

 mass, which is pyramidal in shape, with its longest convex side fitted into the vagus 

 nucleus, its concave side being turned towards, and receiving the post-pyramidal body, 

 becomes the principal nucleus of the auditory nerve. The vagus nucleus is now 

 much diminished in size, and is thrust forwards and wedged in between the newly 

 formed auditory nucleus and that of the hypoglossal. The new mass contains cells 

 of large size, especially at the apex, which projects into the restiform body and into 

 the posterior border of the caput, with both of which it appears to be connected. 



The restiform and p)ost-pyramidal bodies in this region are thickly studded with 

 large cells, and both the vagal and auditory nuclei are bordered by a network, 

 formed by the passage of numerous longitudinal fasciculi, which continue to increase 

 both in size and number as we ascend (Fig. 6"^, I, m). 



The caput cornu through which the large roots of the vagus pass, is thickly 

 studded with cells of medium size. The antero-lateral nucleus is still quite 

 conspicuous, but the cells are separated into more distinct groups, intersected in 

 every direction by the arciform and transverse fibres. Cells are also scattered in 

 the network by which the entire edge of the caput is surrounded, embracing with 

 their processes the large bundles of longitudinal fibres which traverse it. The 

 olivary bodies have now obtained their maximum development, and soon begin to 

 diminish in size with the diminution of the hypoglossal nucleus and roots (Figs. 

 6", 7", 0). In the upper portions of the medulla the remains of the olivary lamina 

 seem to be filled with larger cells, which have replaced the small regular cells of, 

 the lower portions. They still extend across the raphe through the commissure. 



(6.) In the section just above the preceding (Plates I, XIII, Figs. 7, 7") the 

 hypoglossal nucleus, though still large, contains but few cells, and these very much 



