THE CRANIAL OR ENCEPHALIC NERVES. 



815 



substance which in part closes the occipito-spheno-temporal hiatus, and divides it 

 into several particular foramina. Its superior face is covered by the dura mater, 

 and sends a number of filaments to that membrane. 



The Gasserian gangUon is not continued by a single trunk, but immediately 

 divides into two thick branches, one of which leaves the cranium by the foramen 

 ovale — an opening formed by the above-named hiatus ; while the other is lodged 

 in the external fissure in the intra-cranial surface of the sphenoid bone, and passing 

 along it as far as the entrance to the supra-sphenoidal foramina, bifurcates. 



Hence it results that the trigeminus is divided — even at its origin — into three 

 branches : two superior — the oph- 

 thalmic branch of Willis, and the 

 superior maxillary nerve, commenc- 

 ing by the same trunk ; and an 

 inferior, which constitutes the in- 

 ferior maxillary nerve. 



Motor or small root (Fig. 426, 

 8). — This is a flattened band which 

 emerges from the pons Varolii, at 

 the inner side of the principal root. 

 Its fibres may be easily followed to 

 the interior of the pons Varolii 

 (Fig. 451, M'A') ; they disappear 

 in the nucleus of grey substance 

 situated inside the nucleus of the 

 principal sensitive root, near the 

 floor of the fourth ventricle (MA). 

 Leaving the pons Varolii, this root 

 passes forwards on the inferior face 

 of the Gasserian ganglion, which it 

 crosses in a diagonal manner out- 

 wards, and beyond which it inti- 

 mately unites with the fibres of the 

 inferior maxillary nerve. The 

 superior maxillary nerve and the 

 ophthalmic branch do not receive 

 any fibres from it. In the fifth 

 pair, then, it is only the inferior 

 maxillary nerves which are at the 

 same time sensitive and motor, and 

 are real mixed nerves. 



A, Ophthalmic Branch (or 

 Nerve of Willis) (Fig. 450, 1).— This is the smallest of the three divisions 

 furnished by the Gasserian ganglion ; it proceeds by a trunk common to it and 

 the maxillary nerve, which will be described hereafter. This branch enters the 

 smallest of the large supra-sphenoidal foramina, along with the common and ex- 

 ternal oculo-motor nerves, and in the interior of this bony canal it divides into 

 three ramuscules, which reach the bottom of the ocular sheath by the orbital hiatus. 



These ramuscules are : 



1. The frontal or supra-orbital {supra-trochlear) nerve. 



2. The lachrymal nerve. 



LATERAL VIEW OF THE MEDULLA OBLONGATA, SHOW- 

 ING THE ARRANGEMENT OF THE FIFTH PAIR, AND 

 RELATIVELY OF THE MOST IMPORTANT NUCLEI. 



Py, Pyramidal tract ; Gf, genu facialis, or bend of the 

 facial nerve ; Os, superior olivary body ; 0, inferior 

 ditto ; Py.Kr, decussation of pyramids. The nuclei, 

 situated near the middle line, are darker tinted. 

 The numerals represent the roots of the cranial 

 nerves, according to their number. 



