NERVOUS SYSTEM. 



accepted by nearly all writers upon diseases of the nervous system and may be regarded 

 as settled ; and the only question is, how far they can be explained by the anatomy of 

 the parts. 



As we have just seen, the fibres of origin of the facial have been traced to the floor 

 of the fourth ventricle, where a few decussate, but the rest are lost. The question now 

 is, whether or not the fibres pass up through the pons and decussate above, as the patho- 

 logical facts just noted would seem to indicate. Anatomical researches upon this point 

 are entirely unsatisfactory ; and the existence of such a decussation has never been clearly 

 demonstrated. The pathological observations, nevertheless, remain ; and, however indefi- 

 nite anatomical researches may have been, there can be no doubt that lesions in one-half 

 of the pons affect the facial upon the same side, while lesions above have a crossed 

 action. The most that we can say upon this point is, that it is a reasonable inference 

 from pathological facts that the nerves decussate anterior to the pons. 



It will be only necessary to describe in a general way the course of the fibres of dis- 

 tribution of the facial. The main root of the facial, the auditory nerve, and the delicate 

 intermediary nerve of Wrisberg pass together into the internal auditory meatus. At the 

 bottom of the meatus, the facial and the nerve of Wrisberg enter the aquaaductus Fallopii, 

 following its course through the petrous portion of the temporal bone. In the aqueduct, 

 the nerve of Wrisberg presents a little ganglioform enlargement, of a reddish color, which 

 has been shown to contain nerve-cells. The main root and the intermediary nerve then 

 unite and form the common trunk of the facial, which emerges from the cranial cavity 

 by the stylo-mastoid foramen. 



In the aquseductus Fallopii, the facial gives off numerous branches, as follows : 



1. The large petrosal branch is given off at the ganglioform enlargement and goes 

 to Meckel's ganglion. 



2. The small petrosal branch is given off at the ganglioform enlargement or a very 

 short distance beyond it, and passes to the otic ganglion. 



3. A small branch, the tympanic, is distributed to the stapedius muscle. 



4. The chorda tympani, a branch of great physiological interest, passes through the 

 cavity of the tympanum and joins the lingual branch of the inferior maxillary division 

 of the fifth as it passes between the two pterygoid muscles, with which nerve it becomes 

 closely united. 



5. Opposite to the point of origin of the chorda tympani, a communicating branch 

 passes between the facial and the pneumogastric, connecting these nerves by a double 

 inosculation. 



The five branches above described are given of in the aquseductus Fallopii. The fol- 

 lowing branches are given off after the nerve has emerged from the cranial cavity : 



1. Just after the facial has passed out at the stylo-mastoid foramen, it sends a small 

 communicating branch to the glosso-pharyngeal nerve. According to Sappey, this 

 branch is sometimes wanting. 



2. The posterior auricular nerve is given off by the facial a little below the stylo- 

 mastoid foramen. Its superior branch is distributed to the retrahens aurem and the 

 attollens aurem. In its course, this nerve receives a communicating branch of consider- 

 able size from the cervical plexus, by the auricularis magnus. It sends some filaments 

 to the integument. The inferior, or occipital branch, the larger of the two, is dis- 

 tributed to the occipital portion of the occipito-frontalis muscle and to the integument. 



3. The digastric branch is given off near the root of the posterior auricular. It is 

 distributed to the posterior belly of the digastric muscle. In its course, it anastomoses 

 with filaments from the glosso-pharyngeal nerve. From the plexus formed by this anas- 

 tomosis, filaments are given off to the digastric and to the stylo-hyoid muscle. 



4. Near the stylo-mastoid foramen, a small branch is given off, which is distributed 

 exclusively to the stylo-hyoid muscle. 



5. Near the stylo-mastoid foramen, or sometimes a little above it, a long and exceed- 



