THE EVIDENCE OF THE RESPIRATORY APPARATUS 155 
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! 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 muscylature 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 IIIrd (oculomotor), IVth (trochlearis), and VIth (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. 
