814 



THE NERVES. 



pletely as possible ; and in this description we will include the study of the cephalic 

 ganglia of the great sympathetic system, which ought to be regarded as annexes 

 of the fifth pair. 



Origin. — The trigeminus belongs to the category of mixed nerves, as it 

 possesses two roots — ^one sensitive, the other motor. 



Sensitive root (Fig. 426). — This is the largest root. It emanates from the 

 outside of the pons Varolii, near the middle cerebellar peduncle, and is directed 

 forward and downward to gain the anterior portion of the foramen lacerum, 

 where it terminates in a very large semilunar enlargement — the Gasserian ganglion. 

 Flattened above and below, and wider in front than behind, this root on the 

 outer side is about | of an inch in length, but the inner side is double that 

 measurement, because of the oblique position of the gangUon which continues it. 



If it be traced into the substance of the pons Varolii, it will be found that the 

 fibres of the latter separate for its passage from the deep plane it at first occupies. 



Fig. 451. 



DIAGRAM OF A SECTION OF THE PONS VAROLII OF MAN, AT THE ISSUE OF THE FIFTH PAIR 

 OR TRIGEMINAL NERVE. 



PP, Pyramids ; Pr, transverse fibres of the pons Varolii, with stratification of the grey substance ; TT, 

 grey substance in the floor of the fourth ventricle (locus cceruleus) ; CP, gelatinous substance of 

 Rolando; T, ascending roots of the trigeminus, curving to emerge from the pons — great or 

 sensitive root of the trigeminus ; MA, motor nucleus of the trigeminus ; M'A', small root or motor 

 root of the trigeminus (masticator nerve) ; T', fifth pair at its emergence ; x, x, raph^. 



The following is the manner in which it comports itself in this plane : This root is 

 separated into two orders of fibres — posterior and anterior. The first pass beneath 

 the arcif orm fasciculi of the pons VaroHi, to be continued with the grey mass in the 

 medulla oblongata (Fig. 451, CP), which here represents the superior grey cornu 

 of the spinal cord ; the others, anterior, separate from each other, and soon 

 become confounded with the mass of cells in the interior of the isthmus, on the 

 walls of the aqueduct of Sylvius. Others, finally, reach the locus cmrulms (TT) — 

 a portion of the grey substance on the floor of the fourth ventricle. The sensi- 

 tive nucleus of the trigeminus extends from the pons Varolii to the neck of the 

 medulla oblongata ; it is very long (Fig. 452, F, F', F')- The fibres of the 

 trigeminus — or the cells which receive these fibres — are in communication with 

 several cranial nerves, particularly the pneumogastric, glosso-pharyngeal, facial, 

 and auditory (Fig. 452). 



Semilunar or Gasserian ganglion (Fig. 425, 18).— This ganglion, which receives 

 the sensitive root of the trigeminus, is crescent-shaped, its concavity being turned 

 backwards and inwards. It may be said to be embedded in the fibro-cartilaginous 



