16 GRAY SUBSTANCE OP THE MEDULLA OBLONGATA. 



the anterior spinal roots which can be traced into the anterior commissure of the 

 spinal cord. 



Some of the fibres of the hypoglossal roots, especially those lying along the inner 

 edge of the bundle nearest the raphe, turn off either just before or immediately 

 after they enter the broad band of marginal fibres, and pursuing the same covirse, 

 proceed towards the raphe, where they decussate with their feUows from the opposite 

 side. Schroder van der Kolk is undoubtedly right in his assertion that the great 

 loops of decussating fibres figured by KoUiker, and named by Lenhossek ansa hypo- 

 glossi, are formed not from the hypoglossal roots, but by the band of border fibres 

 described above, which he has clearly sho^vir to be derived from the vagus, and as 

 he has also pointed out, this adds greatly to the difiiculty of deciding the question. 

 Most of the fibres forming the hypoglossal roots imdoubtedly penetrate deeply into 

 the nucleus, as maintained by Schroder van der Kolk, but a careful and repeated 

 examination especially with high powers, has convinced me that some of them turn 

 aside, and that a direct decussation exists of a few at least of the root bundles. In 

 the cat, especially in the lower part of the hypoglossal nucleus, the course 

 pursued by the roots is very distinct, and quite numerous bundles may be traced, 

 accompanying the marginal fibres derived from the spinal accessory to the raphe ; 

 higher up the course is somewhat more obscure, as the band proceeding from the 

 vagus is so much broader and more prominent than that from the accessory. 



The roots of the hypoglossal are brought into intimate relation with those of the 

 vagus, by means of a group of large multipolar cells, situated just within the mar- 

 ginal band of fibres proceeding from the vagus roots, by which the hypoglossal 

 nucleus is inclosed (Plate X, Fig. 37, Plate XI, Fig. 40, b). Most of these cells 

 are grouped together just behind the entrance of the hypoglossal roots, and thrust 

 out some of their processes into the anterior columns? embracing the longitudinal 

 columns, with some of the fibres of which they are perhaps continuous. They are 

 connected by the remaining processes with the marginal fibres derived from the vagus 

 (Plate X, Fig. 37, B), and with the hypoglossal roots (A), and also send fibrfs for- 

 ward which decussate at the raphe. This group further serves to connect the mar- 

 ginal fibres with the deeper lying cell groups in the hypoglossal nucleus. 



The hj^oglossal and spinal accessory roots are also connected by a corresponding 

 group, but the cells are comparatively few in number, which may probably be 

 accounted for partly by the difi^erent respective situations of the nuclei ; that of 

 the spinal accessory lying so much more behind the hypoglossal, a more direct 

 connection is doubtless established between them, as is the case between the 

 anterior and posterior cornua of the spinal cord. I have however had no difficulty 

 in making out the little group connecting the hypoglossal with the accessory in the 

 human medulla, and in the cat it is very distinct, containing cells quite large and 

 compactly arranged. 



The lowest roots of the hypoglossal are so precisely similar in arrangement and 

 connection to the anterior spinal roots, as to render it somewhat difficult to mark 

 with precision the limit between the highest cervical nerves and the commencement 

 of the hypoglossal. 



