376 ANATOMY OF THE CENTRAL NEEVOUS SYSTEM. 



sparingly imbedded. It is called the tradus solitarius, or combined descend- 

 ing vagus glosso-pharyngeal root. It can be seen in Figs. 334 and 239, lying 

 dorsal to the vagus roots. Only a small part of the entering vagus roots turns 

 caudally into the funiculus solitarius, and enters, after gradually splitting 

 into end-ramifications, into the neighboring gray column. 



This column is, therefoire, the nucleus of the glosso-pharyngeus and a 

 portion of the vagus. S. Kamon y Cajal has recently shown that just at the 

 place where the central canal widens to form the fourth ventricle the two 

 terminal nuclei of the vagus and glosso-pharyngeus nerves approach each 

 other, and, eventually, at the point where it opens, coalesce to one common 

 mass, the nucleus commissuralis. A considerable number of the fibers of 

 the funiculus solitarius cross over to the other side at this point. 



The glosso-pharyngeal nerve sends the larger mass of its fibers to end in 

 the gray matter of the funiculus solitarius, while only a relatively small 

 portion of them branch in that of the floor of the fourth ventricle. Again 

 we have the plan of the sensory nerves: nerve, nucleus of origin in the 

 spinal ganglion; for the nerve-root, ultimate center (sensory vagus center); 

 and the decussated ascending central tract. 



In the floor of the fourth ventricle^ between the vagus center and the median 

 line, lies another small swelling, Clarke's emhieiitia teres, in which may be found, 

 from the frontal end of the hypoglossal center on up to near the origin of the tri- 

 facial, a, slender group of spindle-shaped cells: the nucleus fiinicuJi teretis, Meynert's 

 nucleus medialis. Its importance is as yet unknown. 



The hypoglossus center consists of several groups of ganglion-cells, all 

 bound together by a fine net-work. From its large multipolar cells develop 

 delicate twigs, which, converging like a brush, form a number of small nerve- 

 trunks. From this center there develop fibers, fibrse afferentes, just as from 

 the spinal anterior horns, which cross over the median line; they do not 

 go far over in the other side, however, but extend, after passing the raphe, 

 cerebrally, and within the pons are joined by other fibers (from the facialis 

 center). The combined bundle then passes to the pes cerebri. If this course 

 be, perhaps, a little different from that of the secondary (central) motor 

 tracts in the spinal cord, still it is materially the same: nerve-root, nucleus, 

 decussating tract to pes. 



A net-work which binds the parts of the hypoglossal center together is 

 of especial interest; it occurs only in one other center, the motor oculi. 

 There are, however, no other nerves whose fibers are called into action so 

 simultaneously and harmoniously as those of the hypoglossus in deglutition 

 and those of the oculo-motorius in movements of the eyes. 



However, there is demonstrable in the prolongation of the hypoglossal 

 net-work, immediately under the epithelium of the ventricle, on both sides, 

 a meshed bundle of medullated nerve-fibers from which fibrils are given off 



