THE BRAIN. 521 



the meningeal artery. Its branches of distribution are to the 

 tensor tympani, the tensor palati, and a small one to the chorda 

 tympani. The mucous membrane of the tympanum and the 

 Eustachian tube is also supplied by this ganglion. 



The submaxillary ganglion, which is situated near the sub- 

 maxillary gland, receives branches of communication from the 

 lingual branch of the fifth, chorda tympani, and sympathetic 

 plexus around the facial artery. Its branches of distribution are 

 to the mucous membrane of the mouth and Wharton's duct, also 

 to the submaxillary gland. 



Abducens. This nerve, which has its real origin in the floor 

 of the fourth ventricle, emerges from the cranium by the sphe- 

 noidal fissure, and is distributed to the external rectus muscle. It 

 is a motor nerve, as is shown by the contraction of this muscle 

 when the nerve is stimulated, and by its paralysis when the nerve 

 is divided. 



Paralysis of Abducens. When from any cause this nerve is 

 so injured as to deprive it of its function, the internal rectus, having 

 lost its antagonist, the external rectus, turns the eye inward toward 

 the nose, producing internal strabismus. There may also be some 

 contraction of the pupil, because the radiating fibers of the iris, 

 which cause dilatation of the pupil, are to a certain extent deprived 

 of their innervation, this being supplied from the sympathetic, 

 some of the nerves of which system run along with the abducens, 

 and when this nerve is injured, these sympathetic fibers may also 

 be involved. It is said that the abducens is more frequently im- 

 plicated in fractures at the base of the skull than any other cranial 

 nerve. 



Facial Nerve. The facial nerve leaves the medulla oblongata 

 at the groove between the olivary and the restiform bodies. Its 

 real origin is a nucleus in the floor of the fourth ventricle. It 

 leaves the cranium by the internal auditory meatus, through which 

 and the aqueduct of Fallopius it passes to emerge at the stylo- 

 mastoid foramen. In the older nomenclature, in which there were 

 but nine pairs of nerves, the facial was associated under the name 

 of seventh nerve with the auditory nerve, in company with which 

 it enters the auditory meatus ; the facial, from its firm consistency, 

 being called the portio dura, and the auditory, on account of its 

 opposite quality, being called the portio mollis. 



The facial has a very extensive distribution the muscles of 

 the face and external ear, the stylohyoid, posterior belly of the 

 digastric, the platysma myoides, and the stapedius. It also gives 

 off the chorda tympani, which is distributed to the submaxillary 

 gland and ganglion, to the inferior lingualis muscle, and to the 

 sublingual gland. Besides these it has most important branches 

 of communication with the sympathetic system and with the 

 glossopharyngeal, pneumogastric, and trigeminus nerves. 



