NERVES. 



85 



Fig. 15. 



the brain adheres loosely to the cord, having the cephalo-spinal fluid 

 within it ; and the pia mater closely embraces it. 



3. Nerves. The nerves are cords of the same nervous substance as 

 that which composes the 

 encephalon and spinal 

 marrow ; extending from 

 these parts, and distribu- 

 ted to the various organs 

 of, the. body, many of 

 them interlacing in their 

 course, and forming 

 plexuses: others having 

 knots or ganglions, and 

 almost all vanishing in 

 the parts to which they 

 are distributed. The 

 generality of English 

 anatomists reckon thir- 

 ty-nine pairs of nerves ; 

 the French, with more 

 propriety, forty-two. 

 Of these, nine, accord- 

 ing . to . the English 

 twelve, according to the 

 French- draw their ori- 

 gin from, or are con- 

 nected with, the ence- 

 phalon; and are hence 

 called encephalic nerves ; Shows the under Surface L Bas of the Encephalon freed from 



*! its Membranes. 



and thirty, from the me- 



* . ,. -, A, anterior, B, middle, and c, posterior lobe of cerebrum. a. 



SpinallS ', and The fore part of the great longitudinal fissure, b. Notch be- 

 tween hemispheres of the cerebellum, c. Optic commissure. 

 d. Left peduncle of cerebrum, e. Posterior perforated space. 

 e to i. Interpeduncular space. /, f. Convolution of Sylvian 

 fissure, h. Termination of gyrus fornicatus behind the Sylvian 

 fissure, i. Infundibulum. I. Right middle crus or peduncle 

 C of cerebellum, m, m. Hemispheres of cerebellum, n. Corpora 



mum Dy means OI lOra- aibicantia. o. PonsVarolii, continuous at each side with middle 

 rnina at ir hnP Thpv crura of cerebellum, p. Anterior perforated space, q' . Horizon- 

 be. .Lliey ta i fissure of cerebellum, r. Tuber cinereum. s, *'. Sylvian 

 fissure, t. Left peduncle or crus of cerebrum. 11, u. Optic 

 , .. . , , tracts, v. Medulla oblongata. x. Marginal convolution of the 



behind the longitudinal fissure. 1 to 9 indicate the several pairs of cerebral 



nerves, numbered according to the usual notation, viz., 1. Olfac- 

 tory nerve. 2. Optic. 3. Motor nerve of eye. 4. Pathetic. 5. 

 Trifacial. 6. Abducent nerve of eye. 7. Auditory, and 7'. Fa- 

 cial. 8. Glosso-pharyngeal, S' . Vagus, and8". Spinal accessory 



hence termed 



The encephalic nerves 



emerge from the era- 



are proceedin 

 before to 



first pair or olfactory, 

 distributed to the organ 

 of smell ; the second pair nerve 

 or optic, the expansion 

 of which forms the retina ; the third pair, motores oculi or common 

 oculo-muscular, which send filaments to most of the muscles of the eye ; 

 the fourth pair, trochleares, pathetici or internal oculo-muscular, dis- 

 tributed to the greater oblique muscle of the eye ; the fifth pair, tri- 

 facial, trigemini, or symmetrical nerve of the head, (Bell,) which send 

 their branches to the eye, nose, and tongue ; the sixth pair, abducentes 

 or external oculo-muscular, which are distributed to the abductor or 

 rectus externus oculi ; the facial nerve, portio dura of the seventh pair, 



