2G GRAY SUBSTANCE OF THE MEDULLA OBLONGATA 



crossing each other in every direction, intermingled with nuclei and granules, and 

 forming an inextricable web closely resembling the structure of the substantia 

 gelatinosa in the spinal cord. 



The union of this portion of the nucleus with the post-pyramidal and restiform 

 nuclei appears to be very intimate, numerous fine fibres passing between them. 

 Along its apex fibres also pass forwards, some winding among the longitudinal 

 bundles, others curving around and becoming arciform fibres, whilst quite a large 

 tuft pass anteriorly into the caput cornu. Some fibres uniting with bundles 

 which apparently turn ofi^ from the nerve-roots, loop around the longitudinal 

 fasciculi in every direction, forming a network of fibres containing a few cells, and 

 closely resembling the network formed around the numerous longitudinal bundles 

 in the neighborhood of the tractus intermedio-lateralis as figured byClarke in the 

 cervical region of the spinal cord.' This network is continued anteriorly and antero- 

 laterally out towards the caput, and backwards towards the restiform body. 



From the postero-lateral or intermediate portion of the nucleus, we have the 

 following classes of fibres produced. 1st. Bundles which proceed from the interior 

 portion and pass directly outwards as radiating fibres, winding among the longitu- 

 dinal bundles or turning off with the arciform fibres. 2d. Bmidles which turn off at 

 a more or less acute angle and pass forwards to join the bundles decussating at the 

 raphe. 3d. Very numerous bundles serving to connect the nucleus with the post- 

 pyramidal and restiform nuclei, and with the caput cornu. 4th. Fibres joining 

 cells in the anterior portion of the nucleus. 



Along the back of the nucleus constant indications are met with of single fibres 

 and bundles cut across by the plane of section, many of which are evidently ascend- 

 ing bundles ; some of them turning off from their longitudinal course and passing 

 through the nucleus as transverse fibres, serve probably to connect various part#of 

 the nucleus with the lower portions of the medulla. 



The nucleus is bordered posteriorly by a thick band or commissure of fibres, 

 which is especially distinct in the upper regions of the medulla ; some of its fibres 

 turn downwards and others upwards, but quite a regular band may be traced along 

 the posterior border of the hypoglossal nucleus to the raphe, where it meets and 

 decussates with a similar band coming from the nucleus of the opposite side, not 

 only serving to connect the posterior portions of the vagal nuclei, but also co-ordi- 

 nating to some extent the post-pyramidal and restiform nuclei. 



The Roots. — Clarke has given a very accurate, though brief, description of 

 the general course pursued by the vagus nerve.^ As stated by him, the bundles 

 pass through the caput cornu on their inward course, penetrating the longitudinal 

 fasciculi derived from the root of the trifacial which are inclosed in its substance. 

 I have not, however, been able to trace any direct communication between them, the 

 roots of the vagus passing directly onwards, pursuing apparently an unbroken course. 

 Stilling' states that the roots of the vagus pass both before and behind, as well as 



^ Philos. Trans. 1859. 



^ Philos. Transactions, 1858, 253. 



* Medulla Oblongata, 37. 



