SEVENTH PAIR OF NERVES. 497 



with the medulla oblongata and the crura cerebelli. The 

 Portio Dura, at its origin, is on the inside of the Portio Mollis. 

 Between these cords are one or more small fibres, called 

 Portio Media, which seem to originate very near them, and 

 finally unite with the Portio Dura. 



Each of the seventh pair of nerves, thus composed, proceeds 

 from its origin to the meatus auditorius internus of the tempo- 

 ral bone; there the portio mollis divides into fasciculi, which 

 proceeds to the different parts of the organ of hearing in the 

 manner described in the account of the ear.* 



The Portio Dura enters an orifice at the upper and anterior 

 part of the end or bottom of the Meatus Auditorius Inter- 

 nus. This orifice is the commencement of a canal, which has 

 been called the Aqueduct of Fallopius, and proceeds from the 

 Meatus Auditorius Internus to the external foramen, between 

 the mastoid and styloid processes at the basis of the cranium. 

 This canal first curves backwards and outwards, near to the 

 upper surface of the petrous bone, then forms an acute angle, 

 and proceeds, (backwards and downwards,) to the stylo-mas- 

 toid foramen, passing very near the cavity of the tympanum 

 in its course. 



The Portio Dura, as it passes into the canal from the meatus 

 internus, seems to receive an investment from the dura mater. 

 It fills up the canal, but does not appear to be compressed. 

 Near the angle it is joined by the twig of the Vidian nerve, 

 which proceeds from the pterygoid branch of the fifth pair and 

 enters the petrous bone by the small foramen innominatum on 

 its anterior surface. In its course through the canal it sends 

 off some very small twigs to the muscles and appurtenances of 

 the small bones of the ear, and to the mastoid cells ; and, when 

 it has arrived almost at the end of the canal, it sends off in a 

 retrograde direction, a small branch which proceeds into the 

 cavity of the tympanum, (entering it by a foramen near the 

 base of the pyramid,) and crosses the upper part of it, near the 

 membrana tympani, between the long processes of the Malleus 

 and Incus. This twig is the Chorda Tympani; it proceeds 



* See vol. ii. p. 469. 



42* 



