334 THE FOURTH, FIFTH, AND SIXTH PAIRS. 



OF THE FOURTH PAIR, PATHETICI, OR TROCHLEAR NERVES. 



This nerve arises from the valve of Yieussens, near the testis, and, 

 The fourth pair, passing around the cms cerebri, enters the orbit, and is dis- 

 or pathetic!. tributed to the orbital surface of the superior oblique, or 

 trochlear muscle, for which it is the motor nerve. When it is irritated 

 that muscle is convulsed. 



OF THE FIFTH PAIR, TRIFACIAL, OR TRIGEMINI. 



The fifth nerve has a construction so closely analogous to that of the 

 The fifth pair, spinal nerves, that it has been designated the spinal, nerve of 

 or trigemini. ^he head. It arises by two roots, the anterior of which is 

 the smaller, the posterior having a large ganglion, the ganglion of Gas- 

 ser ; with this ganglion the anterior root is in contact, but not in con- 

 nection: it passes forward to the inferior maxillary nerve. From the 

 ganglion three branches diverge, the ophthalmic, the superior maxillary, 

 and inferior maxillary, the first proceeding from the upper angle of the 

 ganglion, the second from the middle, the third from the inferior angle. 

 This last receives the motor portion of the nerve ; the first and second 

 branches are sensory, the third is sensory and motor also. From the 

 sensory portions the anterior and most of the antero-lateral portions of 

 the head are furnished, as also the organs of special sense themselves, so 

 far as their common sensation is concerned. The motor branch supplies 

 the muscles of mastication. 



OF THE SIXTH PAIR, OR ABDUCENTES. 



This nerve arises by several filaments from the upper part of the cor- 

 The sixth pair, pus pyramidale, near to the pons varolii, and is distributed 

 or abducentes. to tne external rectus. From its origin, distribution, and 

 from experiments made upon it, it is known to be a motor nerve. 



ILLUSTRATIONS OF THE THIRD, FOURTH, FIFTH, AND SIXTH PAIRS OF NERVES. 



Fig.\\\ 1, chiasm of optic nerves; 2, 

 third pair ; 3, nasal nerve ; 4, external oculo- 

 motor; 5, ganglion of Gasser; 6, nasal nerve 

 and its two branches, internal and external ; 

 7, nerve of obliquus inferior ; 8, ophthalmic 

 ganglion ; 9, ciliary nerves ; #, portion of ld- 

 vator palpebrae superioris and rectus superi- 

 or ; , rectus inter nus ; c, rectus extern us ; d, 

 fibrous ring of the recti muscles. 



NERVES IN THE ORBITAL CAVITY. 



NemTs of the orbit. Fig. 162 i 1, 1, optic nerve and globe of the 



