40 GRAY SUBSTANCE OP THE MEDULLA OBLONGATA 



fibres pursue their vertical course behind the olivary body, turning ofi" at various 

 angles to penetrate the lamina, joining the cells here or passing among them to 

 more distant parts. The olivary column is terminated above by a group of large, 

 multipolar cells scattered in the network about the raphe, which have replaced 

 the smaller olivary cells, and measure about ^^-^ to -^^-^ of an inch in diameter. 



The connection between the olivary bodies and the nuclei of the hypoglossal is 

 much more apparent in the sheep than in man. Little bundles of fibres are con- 

 stantly seen running from the nucleus on each side the raphe and close to it towards 

 the olivary body, and these bundles are commonly studded throughout their entire 

 course with small scattered cells and little cell-groups. In some specimens the 

 hypoglossal nucleus on each side of the raphe sends out a little pointed promontory 

 of some length containing cells, and along the raphe cell-groups are formed on each 

 side at regidar intervals, exactly opposite each other, connecting the hypoglossal 

 nuclei with the olivary bodies (Figs. 2", 6", 7"), while branching off from the apex 

 of the hypoglossal nucleus, similar little ceU-groups are found, connecting it with 

 the antero-lateral nucleus (Figs. 4", 19"). 



In the cat and the carnivora generally, the anterior pyramids are deeper, and 

 approach more nearly to the human type, the olivary bodies are much more fully 

 developed and present a more decidedly convoluted form, which is occasionally very 

 marked ; they are stiU, however, as in the sheep, situated just behind the pyramids, 

 close to the middle line, the hypoglossal roots running on the outside. Their posi- 

 tion may be seen in Plate IX, Fig. 33, though as this section is from the upper 

 part of the medulla, they have already begun to diminish in size and in the number 

 of convolutions. The cells of the lamina in the cat are quite small, measuring 

 about ^oVt of an inch in diameter ; they appear to follow more closely the direction 

 and form of the convolutions than in the sheep, being arranged within the lamina 

 much in the same way as in man, while in the sheep, as stated above, the cells 

 follow more nearly the direction of the arciform fibres, the layer of ceUs often cross- 

 ing the lamina at right angles with the direction of the folding. 



Schroder van der Kolk^ has stated, that in all animals the inferior olivary bodies 

 are situated within the limits of the hypoglossal roots, but this does not appear to 

 be strictly true, since in the sheep we find distinct traces of the convolution after 

 the disappearance of the hypoglossal roots (Fig. 7"), and in the cat, this is also 

 distinctly seen to be the case (Fig. 33), evident remains of the olivary body, still 

 showing the convoluted structure, being found on a level with the roots of the 

 glossopharyngeal. The same is true in the human medulla, the convolutions are 

 distinctly seen in Fig. 24", and can be traced for a considerable distance above, as 

 may be seen by reference to Stilling's admirable plates (Pons Varolii, Plate i). I 

 have not been able to trace any direct communication between the accessory or 

 vagal nuclei and the olivary bodies, nor any direct connection with the hypoglossal 

 roots, though the latter often pass directly through the outer portion of the olivaries. 



' Medulla Oblongata, 164. His deductions seem to have been principally founded on external 

 measurements, which of course are liable to error. 



