ON THE NERVES IN GENERAL. 487 



double roots, one arising from the anterior column and the 

 other from the posterior column of the spinal marrow; these 

 are the spinal nerves, the sub-occipital and the trigemini, or 

 the fifth pair of the cranial nerves. These nerves serve at the 

 same time for sensibility and for muscular motion. 2d, Into 

 nerves with a single root: these are the first, second, and 

 eighth* pairs, or the olfactory, optic, and auditory nerves; and 

 the third, fourth, and sixth, or the motor nerves of the eye; 

 and the twelfth or the motor nerves of the tongue. These 

 nerves serve exclusively, some for sensibility, the others for 

 muscular motion. 3d, Into respiratory nerves, vocal, and of 

 expression: they arise from the lateral fascicle of the superior 

 part of the spinal marrow; these are, according to Ch. Bell,t 

 to whom we owe an exact knowledge of them, the par vagum, 

 which is the centre of this system, the facial nerve, the glosso- 

 pharyngeal, the spinal or accessory, the diaphragmatic, and 

 the external thoracic. 4th, Into circulatory nerves: they arise 

 from all the spinal nerves; these are the great sympathetic 

 nerves. These last and the par vagum are connected besides 

 with the interior tegument, with the glands and the interior 

 muscles in general. The sympathetic nerve will be described 

 separately in the following section. 



772. The form of the nerves is, in general, cylindrical. 

 Their branches are, as in the vessels, larger taken together 

 than the trunks which furnish them: the nerves consequently 

 enlarge from their origin to their termination; they also swell 

 a little at their origin. Their surface presents wrinkles or 

 transverse striae, which depend on the elongation which they 

 experience in different movements; these wrinkles are easily 

 perceived with a lens, especially in the nerves of the mem- 

 bers. 



There are three things to consider in the nerves; 1st, their 

 origin; 2d, their course; 3d, their termination. 



773. We must not understand by origin of nerves, the 



* This must be a mistake that our illustrious author has overlooked while 

 correcting the proof; for the auditory nerve is the seventh and not the 

 eighth pair. TBAKS. 



f Phil Trans. 1822, part 1 and 2. 

 63 



