Chap. 28.] [ 279 ] 



CHAP. XXYIII. 



STRUCTURE AND GENERAL DISTRIBUTION OF 

 THE NERVES. 



Origin of the Nerves. Extreme fubttlty of the Nervous Fibres. 

 Ganglions. Plexus. Fontana 1 s Microfcopical Obfervatiom on 

 Nerves.- Nerves from the Braia. OlfaJlory and Optic Nerves, 

 &c . Auditory Nerves, &c. Lingual Nerves, &c. Sympathetic 

 Nerve.-^Nerves from the Spinal Marrcnv. Phrenic Nerve.--* 

 Lkrfal and Brachial Nerves, &c. Lumbar and Crural Nerves, 

 ff<r. Sciatic Nerve. 



NERVES are white cords diftributcd from 

 the brain over the whole body j they rife, as 

 was intimated in the preceding chapter, either imme- 

 diately from the brain, or mediately from it by means 

 of the fpinal marrow, which is itfelf a continuation of 

 the fibres of the brain, and might without impro- 

 priety be confidered as the largeft nerve in the body. 

 The nerves, as they pafs off from the brain and fpinal 

 marrow are ir.vefted, and collected into firm cords, by 

 the dura and pia mater. The former, however, is foon 

 r effected back, but the latter accompanies them through 

 all their ramifications, and is fuppofed to be only 

 thrown afide where they terminate in their fentient ex- 

 tremities. 



As the medullary fibres are obferved to decollate 

 each other in different parts of the brain, and as inju- 

 ries of one fide of the head have often been obferved to 

 produce a palfy of the oppofite fide of the body, it 

 has been fuppofed that all the nerves originate from the 

 fide of the brain oppofite to that at which they come 

 out. This opinion, however, is far from being efta- 

 T 4 bliftied, 



