HUMAN AND MAMMALIAN. 25 



ingly numerous, especially in the anterior portion of the nucleus, where they are 

 very closely crowded together. The larger cells are found chiefly in the anterior 

 and antero-lateral portions, in the neighborhood of the hypoglossal nucleus and 

 near the entrance of the vagus roots ; those lying further inwards, more especially 

 in the posterior and postero-lateral portions of the nucleus and iii the neighborhood 

 of the caput comu and post-pyramidal nucleus are mostly quite small and are oblong 

 or fusiform in shape. 



The cells measure as follows, the measurements being made on their longest 

 diameter and as near as possible to the point where the nucleus attains its greatest 

 development. In the medulla of the sheep, the cells in the anterior part of the 

 nucleus measure from gig to -j-i^ of an inch, and in the posterior portion 2 oVo to 

 In man 1/33 *^ e^ie *^^ ^^ inch, the smaller cells measuring 

 In the cat, about ygVs" ^^ ^^ inch. 



The group of cells represented in Plate X, Fig. 38, is from the anterior portion 

 of the vagus nucleus ; F, the bundle of vagus roots, many of which pass inwards to 

 the cell group. Intermingled with the larger cells are very numerous smaller ones, 

 and many of exceedingly small size with numberless single nuclei (not represented 

 in the figure) are found scattered throughout the entire substance of the nucleus. 

 It is quite impossible to determine the nature of these very small cells ; they closely 

 resemble those found in the posterior cornua of the spinal cord, and some of them 

 are probably fragments of larger nerve cells, or cells which are still undeveloped, 

 whilst many doubtless belong to the connective tissue. 



The cell processes pass out in various directions, both transversely and longitudi- 

 nally ; many of them are directly continuous with the nerve roots, whilst others run 

 in the direction of the neighboring hypoglossal nucleus, and are continuous either 

 with processes from its cells, or with the nerve-roots themselves {A, A\ thus form- 

 ing connections analogous to those which I formerly demonstrated between the 

 anterior and posterior cornua of the spinal cord.^ A third set send their processes 

 transversely into the antero-lateral columns, embracing the numerous longitudinal 

 fasciculi which pass upwards ia the bifurcation of the nucleus. Many cells 

 serve also to connect the nucleus with the caput cornu, establishing thereby 

 a possible relation between the vagus and the trifacial, the nucleus of which 

 has been shown by Clarke to send descending fibres into the numerous longitudinal 

 bundles by which the caput is pierced, a statement which I have been able thoroughly 

 to verify. Other processes pass backwards, and serve to connect the roots as well 

 as the anterior portions of the nucleus with the deeper lying parts, and also directly 

 or through the iatervention of cells, with the post-pyramidal and restiform nuclei. 



As mentioned above, the vagus nucleus seems to consist of two more or less dis- 

 tinct portions (Plates XIII, XV). The anterior portion, divided from the posterior 

 by the great bundles of longitudinal fibres (l), is for the most part occupied by a 

 very large and closely crowded group of cells (F) with which many of the vagus 

 roots are connected ; the posterior part of the nucleus contains but very few cells, 

 mostly of exceedingly small size, its substance being chiefly made up of fine fibres 



* Memoirs of the American Academy, 18G1, 10. 



