32 DISSECTION OF THE HEAD. 



orbit. And the last, or the inferior maxillary nerve, passes through the fora- 

 men ovale to reach the lower jaw, the lower part of the face, and the tongue. 



The smaller root, entering the same tube of the dura mater as the large 

 one, passes beneath the ganglion, without communicating with it, and joins 

 only one of the three trunks derived from the ganglion : if the ganglion be 

 raised, this root will be seen to enter the inferior maxillary nerve. 



Those branches of the ganglion which are unconnected with the smaller 

 or motor root, viz., the ophthalmic and superior maxillary, are solely nerves 

 of sensibility ; but the inferior maxillary, which is compounded of both 

 roots, is a nerve of sensibility and motion. But the whole of the inferior 

 maxillary nerve has not this double function, for the motor root is mixed 

 almost exclusively with the part which supplies the muscles of the lower 

 jaw ; and it is, therefore, chiefly that small piece of the nerve which pos- 

 sesses a twofold action, and resembles a spinal nerve. 



The ophthalmic nerve is the only one of the three trunks which needs a 

 more special notice in this stage of the dissection. It is continued through 

 the sphenoidal fissure and the orbit to the forehead. In form it is a flat 

 band, and is contained in the wall of the cavernous sinus below the third 

 and fourth nerves. Near the orbit it divides into three branches (p. 51). 



In this situation it is joined by filaments of the cavernous plexus of the 

 sympathetic, and gives a small recurrent filament (fig. 4, f) to that part of 

 the dura mater which forms the tentorium cerebelli (Arnold). 



The SIXTH NERVE (fig. 4, 6 ) enters the orbit through the sphenoidal fis- 

 sure, and supplies one of the orbital muscles. It pierces the dura mater 

 behind the body of the sphenoid bone, and crosses the space of the caver- 

 nous sinus, instead of lying in the outer wall with the other nerves. 



In the sinus the nerve is placed close against the outer side of the 

 carotid artery ; and it is joined by one or two large branches of the sym- 

 pathetic nerve surrounding that vessel. 



SEVENTH NERVE according to Willis (fig. 4, 7 ). This cranial nerve 

 consists of two trunks, fascial and auditory, and both enter the meatus 

 auditorius internus. In the bottom of the meatus they separate : the facial 

 nerve courses through the aqueduct of Fallopius to the face, and the audi- 

 tory nerve is distributed to the internal ear. 



EIGHTH NERVE (fig. 4, 8 ). Three trunks are combined in the eighth 

 cranial nerve of Willis, viz., glosso-pharyngeal, pneumogastric, and spinal 

 accessory. All three pass through the central compartment of the foramen 

 jugulare, but all are not contained in one tube of the membranes of the 

 brain. The glosso-pharyngeal nerve is external to the other two, being 

 separated from them by the inferior petrosal sinus, and has distinct sheaths 

 of the dura mater and the arachnoid membrane ; but the pneumo-gastric 

 and spinal accessory nerves are inclosed in the same tube of the dura 

 mater, only a piece of the arachnoid intervening between them. 



The NINTH NERVE (fig. 4, 9 ) is the motor nerve of the tongue, and con- 

 sists of two small pieces, Avhich pierce separately the dura mater opposite 

 the anterior condyloid foramen; these unite after passing through that 

 aperture. 



Dissection. The dissector may now return to the examination of the 

 trunk of the carotid artery as it winds through the cavernous sinus. 



On the opposite side of the head, viz., that on which the nerves in the 

 wall of the cavernous sinus are untouched, an attempt may be made to find 

 two small plexuses of the sympathetic on the carotid artery, though in an 

 injected body this dissection is scarcely possible. 



