30 GRAY SUBSTANCE OF THE MEDULLA OBLONGATA. 



CHAPTER VI. 



THE GLOSSOPHARYNGEAL NUCLEUS AND ROOTS. 



The form and development of the glossopharyngeal nucleus, and the general 

 course of its nerve-roots in the human medulla, have been described by Stilling' 

 with very considerable accuracy. More recently Clarke^ has given a detailed 

 description of the course of the fibres within the nucleus, to which but little remains 

 to be added. 



The course of the glossopharjaigeal roots, and the distribution of their fibres 

 within the nucleus resembles very strikingly the course and distribution of the vagus 

 roots as described above, and the connection between these two nuclei is very close, 

 the nucleus of the vagus passing gradually forwards as that of the auditory makes 

 its appearance, until the three nuclei (hypoglossal, vagus and auditory) are fused 

 as it were into one mass, the remains of the vagus nucleus now constituting one of 

 the sources from which the glossopharyngeal roots are derived. The transition, 

 however, between the vagal and glossopharyngeal roots or nuclei is so gradual, that 

 it is quite impossible to point out any exact line of demarcation. 



In the sheep the glossopharyngeal roots pass inwards in two or three bundles, 

 which, after crossing the arciform plexus, often subdivide into as many as six or 

 eight smaller ones, penetrating the caput cornu on their way to the nucleus. In the 

 cat and in man the main bundles, usually not more than two or three in number, 

 pass inwards without subdividing, till they reach the apex of the nucleus (Plate VI, 

 Fig. 24) Avhich a portion of them enter, other portions of the bundles diverging, 

 and the fibres spreading out in various directions either forwards or backwards, 

 passing, as Clarke has noticed, among the longitudinal fasciculi which adjoin the 

 margin of the nucleus. Some of the fibres pass into the loose netw:ork formed from 

 the remains of the posterior pyramid, others pass forwards towards the remains of 

 the hypoglossal nucleus. Some of the fibres, as mentioned above, proceed directly 

 inwards, joining the group of rather large cells which constitutes the remains of the 

 vagus nucleus. The cells near the apex are mostly very small, but further inwards, 

 near the back of the little nucleus, measure about j-g\-^ to -^^-^ of an iach in length ; 

 in the human medulla they are mostly obovate or fusiform, resembling the vagus, 

 cells, and are evidently connected with a portion of the glossopharyngeal roots. 



As in the case of the vagus, a large anterior bundle is formed, which turns ofi^ at 

 or near the apex of the nucleus, and as described by Clarke, " turns inwards round 



» Medulla Oblongata. = Philos. Trans. 1858. 



