42 GRAY SUBSTANCE OF THE MEDULLA CTELONGATA. 



of the caput cornu, but are more commonly an offshoot from the main nucleus, 

 with which they are evidently closely connected (Figs. 2", 3", 4", 6"). In the cat 

 the cells of the antero-lateral nucleus are very conspicuous and well defined, they 

 are collected into a group in the same situation as in the sheep, but form a rather 

 more open plexus or network with the arciform fibres, many of Avhich are distinctly 

 seen to be continuous with their processes. As cell-processes also pass in many 

 different directions transversely as well as longitudinally, this group doubtless serves 

 to connect the arciform fibres with the other parts of the medulla, constituting 

 apparently an accessory nucleus to each olivary body. 



Its connections with the caput cornu have already been pointed out ; and connec- 

 tions are also established between this nucleus and that of the hypoglossal, and with 

 the vagal and spinal accessory nuclei ; with the two latter sometimes directly, and 

 sometimes through the caput. The connections established between the antero- 

 lateral nucleus and that of the hypoglossal are often very striking. They are espe- 

 cially evident in the sheep, in which I have often noticed the formation among the 

 border fibres of the hypoglossal nucleus, of a little cell-group, sometimes thrust 

 out along the course of the roots for a considerable distance, and joined by scattered 

 cells to quite a large, elongated group of stellate and oval cells, which are evidently 

 a prolongation obliquely inwards of the antero-lateral nucleus (Fig. 4"). Along the 

 raphe on each side, little cell-groups are found at varying distances, each of which 

 is usually provided on the opposite side with its exact covinterpart, and these little 

 groups are apparently entered by numerous fibres from the arciform plexus, which 

 have just passed through the nuclei mentioned above. 



In the human medulla the antero-lateral nucleus is quite conspicuous (Figs. 18", 

 19", 20", 21", 22", 23") ; the cells are rather smaller than in the sheep, measuring 

 about j-jj^o to j^^ of an inch. The relations between the antero-lateral nucleus 

 and the other portions of the medulla, are the same in man as those described above 

 in the sheep, and its changes in form and situation have been sufficiently dwelt 

 upon in Chap. II, on the morphology of the human medulla. 



By comparing Figs. 6", 7" with Fig. 8" (all from the sheep) it will be seen that 

 the groups of very large cells, which Avill be subsequently shown to be the origin of 

 the upper olivary bodies, are evidently developed from the remains of the antero- 

 lateral nuclei, so that it is extremely probable that the antero-lateral nucleus is, in 

 the lower part of the medulla, accessory to the olivary column, and that it is con- 

 tinued upward into the trajjezium, where it is developed into the U2:iper olivary 

 body, the structiu-e and relations of which will be described subsequently. 



