HUMAN AND MAMMALIAN. 1] 



deeply bifurcated by the longitudinal fasciculi spoken of above (I), and sends for- 

 ward one of its spurs into the substance of the post-pyramidal body. Between the 

 post-pyramidal nucleus and that of the vagus a new body has arisen, apparently 

 developed out of the substance of both nuclei. This new body (Fig. 22, A), the 

 formation of which has been described very accurately by Clarke,^ becomes the prin- 

 cipal nucleus of the auditory nerve, and is at first intimately connected both with 

 the post-pyramidal and vagal nuclei. It presents the usual pyriform or triangular 

 shape assumed by the other nuclei, and contains numerous scattered cells of varied 

 form and dimensions. It seems to be inserted like a wedge between the vagus 

 nucleus and that of the post-pyramidal body, the latter being partially blended with 

 it and partly pushed aside, and is already pierced to some extent by little bundles 

 of longitudinal fibres (to), appearing in the section as dark spots, which continually 

 increase as we ascend, forming eventually a very remarkable marginal network, con- 

 taining numerous cells, many of which are of large size, and embrace the longitudi- 

 nal fasciculi in all directions with their processes. 



(8.) These changes are still more evident higher up (Figs. 23, 23"), and have been 

 exceedingly well figured both by StUling^ and Clarkel The vagus nucleus ( F) is 

 here rapidly thrust forward by the extension of the nucleus of the auditory, and 

 soon becomes the nucleus of the glosso-pharyngeal, which is simply an upward 

 extension of that of the vagus, between which and the glosso-pharyngeal it is 

 impossible to fix any definite boundary. 



The remains of the hypoglossal nucleus are quite conspicuous, and the place of 

 the root is occupied by transverse, radiating fibres (XIT), running apparently into 

 the hilus of the olivary body, but consisting mostly of obliquely ascending bundles 

 of hypoglossal roots which are cut off by the plane of section. 



The nucleus of the auditory (A) is now considerably extended, and sends out a 

 spur or process into the post-pyramidal body, by means of which it is also brought 

 into connection with the restiform nucleus, as well as with the caput. The bundles 

 of longitudinal fibres (to) by which the auditory nucleus is bounded on its postero- 

 lateral margin, rapidly increase in size and number, and in the sections just above 

 (Figs. 24, 24"), we find them arranged in a wide band or network along the outer 

 edge of the auditory nucleus, of which they constitute the outer portion (A'), 

 containing among the meshes of the network numerous very large multipolar cells. 



(9.) The little nucleus of the glosso-pharijngeal is here seen (Fig. 24", G) thrust 

 very far forward by the extension of the auditory nucleus, which quite overlies the 

 remains of the vagus nucleus ; it is entered by the glosso-pharyngeal roots {IX) in 

 several distinct and wavy bimdles. 



In this part of the medulla (Figs. 24, 24") the entire outline is changed from the 

 circular or somewhat crescentic form presented below, to one much more elongated 

 along the posterior boundary; the restiform columns being drawn apart laterally 

 from the middle line or raphe, so that the nuclei which in the lowest part of the 



' Philos. Transactions, 1858, and Proceedings of the Royal Society, June, 1861. 



" Medulla Oblongata. Atlas, pi. vii, figs. 1—6. 



' Philos. Trans. 1858, pi. xvi, figs. 31, 32; pi. xvii, fig. 36. 



