544 



Dynamic Theory. 



The sixth pair are the Abducentes. This nerve moves the rectus externus, or external 

 straight muscle of the eyeball, which, by its contraction, rolls the eyeball outward. 

 This nerve also supplies the nictitating membrane and the retractor bulbi, in those ver- 

 tebrates which possess those parts. The root of this nerve is in the pyramidal tract of 

 the medulla obi ongata. (See fig. 266.) This nerve leaves the brain through the sphe- 

 noidal fissure. 



Tli 



FIG. 267. 



FIG. 267. Showing Island of Reil, Pons Varolii and Medulla Oblongata, ivith roots of 

 the Encephalic or Cranial nerves, right side. 



//.Optic Nerve running back to e and i. 

 Ill to XII Encephalic Nerves. (See fig. 



St. Upper surface of Corpus Striatum. 

 (7. Convolutions of the Island of Reil (all 

 the cerebrum above this has been removed). 

 Th Back part of the Optic Thalamus. 

 e. External Corpus Geniculatum. 

 i. Internal 



Sy. Fissure of Sylvius in front of Isle of R. 

 p. Pineal Gland. 

 q. Corpora Quadrigemina. 

 v. Valve of Vieussens origin of 4th nerve. 

 a. Right Corpus Albicans, with Infunuibu- 



lum and tuber Cinereum in front, 

 ft. Pituitary gland. 

 P. Cerebral Peduncles. 

 1, Olfactory tract running past the fissure 



of Sylvius. 



266.) 



y and z. Anterior and Posterior Roots 1st 

 Cervical Nerve. 



Pons. Pons Varolii. 



s, ra, in. Superior, Middle and Inferior Pe- 

 duncles of the Cerebellum, cut short. 



o. Olivary body. 



r. Restiform body. 



ar. Arciform fibres. 



tr. Tubercle of Rolando. 



pa. Anterior pyramid. 



ca, cp, cl. Anterior, Posterior and Lateral 

 columns of Spinal Cord. 



( Quain, after Allen Thompson.) 



Seventh pair is the Facial nerve. It is sometimes called the portio dura of the seventh 

 pair. It supplies the superficial muscles and skin of the face, with branches to the pa- 

 vilion of the ear, the hyoidean arch and the jaws. It connects with the brain by two 

 roots, one to the olivary tract, and the other to the corpus restiforme. According to 

 Carpenter, the portion that goes to the face is motor. The sensory fibres that are found 

 with it are thought to be derived from the fifth pair and from the cervical nerves, with 



