THE EVIDENCE OF THE RESPIRATORY APPARATUS 1 55 



continues as the roots of the glossopharyngeal nerve, as the roots of 

 the facial nerve, and as a portion, especially the motor portion, of 

 the trigeminal nerve. Now, all these nerves belong to a well-defined 

 system of nerves, as Charles Bell 1 pointed out in 1830, a system of 

 nerves concerned with respiration and allied mechanisms, such as 

 laughing, sneezing, mastication, deglutition, etc., nerves innervating a 

 set of muscles of very different kind from the ordinary body-muscles 

 concerned with locomotion and equilibration. Also the centres from 

 which these motor nerves arise are well defined, and form cell-masses 

 in the central nervous system, quite separate from those which give 

 origin to somatic muscles. 



This original idea of Charles Bell, after having been ignored for so 

 long a time, is now seen to be a very right one, and it is an extra- 

 ordinary thing that his enunciation of the dual nature of the spinal 

 roots, which was, to his mind, of subordinate importance, should so 

 entirely have overshadowed his suggestion, that in addition to the 

 dorsal and ventral roots, a lateral system of nerves existed, which 

 were not exclusively sensory or exclusively motor, but formed a 

 separate system of respiratory nerves. 



Further, anatomists divide the striated muscles of the body into 

 two great natural groups, characterized by a difference of origin and 

 largely by a difference of appearance. The one set is concerned 

 with the movements of internal organs, and is called visceral, the 

 other is derived from the longitudinal sheet of musculature which 

 forms the myotomes of the fish, and has been called parietal or 

 somatic. The motor nerves of these two sets of muscles correspond 

 with the lateral or respiratory and ventral roots respectively. 



Finally, it has been shown that the segments of which a verte- 

 brate is composed are recognizable in the embryo by the segmented 

 manner in which the musculature is laid down, and van Wijhe has 

 shown that in the cranial region two sets of muscles are laid down 

 segmentally, thus forming a dorsal and ventral series of commencing 

 muscular segments. Of these the anterior segments of the dorsal 

 series give origin to the striated muscles of the eye which are inner- 

 vated by the Illrd (oculomotor), IVth (trochlearis), and Vlth (ab- 

 ducens) nerves, while the posterior segments give origin to the 



1 N.B. — In addition to the nerves mentioned, C. Bell included, in his respiratory 

 system of nerves, the fourth nerve or trochlearis, the phrenic and the external 

 respiratory of Bell. 



