101 



CHAPTER XIX. 



ENCEPHALIC NERVES EXCLUSIVELY MOTOR IN FUNCTION. THE 



THIRD PAIR OF NERVES. THE FOURTH PAIR. THE SIXTH PAIR. 



THE PORTIO DURA OF THE SEVENTH PAIR. THE NINTH PAIR. 



THE nerves which we shall consider in this chapter are purely 

 motor in their function; and, on this account, are conveniently 

 classed together. We shall see, however, that from their occa- 

 sional anastomosis with sensitive nerves, they contain sentient fila- 

 ments which serve to inform the mind of the state of the muscles 

 to which their motor filaments are distributed. 



The Third Pair of Nerves, or Motores Oculorum. These nerves 

 are connected with the crura cerebri. Each nerve emerges from 

 the corresponding crus, on the side of the locus perforatus posticus, 

 or pons Tarini. 



When traced into the substance of the crus, the component fasci- 

 culi of each nerve are seen to diverge from each other, and to sink 

 into the dark vesicular matter constituting the locus niger. Here, 

 no doubt, the filaments connect themselves with the vesicles of this 

 mass of gray matter. 



Each nerve proceeds forwards and outwards, and passes through 

 a canal in that portion of the dura mater which forms the outer 

 wall of the cavernous sinus into the orbit through the spheno- 

 orbital foramen, and just as it has reached this foramen it divides 

 into a superior and an inferior branch, the distribution of which is 

 shewn in the following table. 



( 1. b. To the levator palpebrse superioris. 



A. Superior division. \ 2 ^ TQ the guperior rectus oculi 



1. b. To the internal rectus. 



2. b. To the inferior rectus. 



B. Inferior division. ^ 3. 6. To the inferior oblique. 



1 4. b. To the ophthalmic ganglion, also called the 

 short root of that ganglion. 



The anastomoses of the third nerve take place entirely in that 

 stage of its course in which it lies in the outer wall of the cavernous 

 sinus. They are with the ophthalmic division of the fifth nerve, 

 and with the carotid branch from the inferior cervical ganglion of 



