MUSCULAR MOVEMENTS. 909 



through themselves ; but when the former are deficient, the action of the vocal 

 muscles may be guided by the latter ( 751). 



CHAPTER XVI. 



OF MUSCULAR MOVEMENTS. 



1. General Considerations. 



912. BY far the larger proportion of the Muscular apparatus of the Human 

 Body may be considered in the light of an instrument whereby the Nervous 

 System is enabled to give motion to its parts, and thus to effect those changes, 

 in its relation to the external world, which are requisite for its physical well- 

 being, or which are the expressions of its psychical powers. There is probably 

 no part of the Muscular System which is altogether beyond the pale of Nervous 

 agency ; but a tolerably definite line of demarcation may be drawn, both struc- 

 turally and functionally, between the two primary subdivisions of this system , 

 in the first of which the Muscular Apparatus of Organic Life the actions are 

 but little dependent upon nervous agency ; whilst in the second the Muscular 

 Apparatus of Animal Life scarcely any action takes place but what is called 

 forth by nerve-force. The First group consists of the muscular envelops which 

 surround the various open cavities of the body, and which form part of its ge- 

 neral investment ; its office being to aid in the performance of the Organic 

 functions, by giving motion to the contents of the cavities, or by maintaining a 

 proper state of tension around them ; and it is composed almost entirely of the 

 non-striated or smooth form of muscular fibre, the only marked exception being 

 in the case of the heart. Under this category rank the proper muscular coat of 

 the alimentary canal, from its commencement in the oasophagus to its termina- 

 tion at the anus ; the muscular coats of the gland-ducts which discharge them- 

 selves into this ; the muscular fibres of the trachea and bronchial tubes ; the 

 muscular substance of the heart, and the muscular coats of the bloodvessels and 

 absorbents generally j the muscular walls of the ureters, bladder, urethra, and 

 vasa deferentia in the male, and of the ureters, bladder, urethra, Fallopian tubes, 

 uterus, and vagina of the female ; and finally, the muscular substance of the 

 skin. With regard to nearly all these parts, as already pointed out, it is difficult 

 to obtain evidence that nervous agency has anything to do with their contrac- 

 tions ; and all the evidence yet adduced tends only to show that contractions 

 may be excited through the nervous system, not that they habitually are so ; their 

 ordinary contractions being produced either by their own motility ( 499), or by 

 stimuli directly applied to themselves. The Second of the above-named divisions 

 consists of all those muscles which are usually styled voluntary, since they can 

 be put or retained in action by the mandates of the Will ; but besides these, it 

 includes a large group of muscles (those, namely, that are concerned in the 

 functions of Deglutition, Respiration, Yomiting, Defecation, and Urination), 

 over which the Will exerts only a partial control, their activity being usually 

 called forth automatically. It would seem as if this group were placed under 

 the same conditions, as regards their dependence on Nervous agency, with those 

 more properly termed voluntary, in order that the Will, which is altogether 

 powerless over the Muscular Apparatus of Organic Life, may bring their opera- 

 tions into harmony with the general requirements of the system; the functions 

 in question being those which constitute (so to speak) the meeting-points be- 

 tween the Organic and Animal life. For as we descend the scale of animal 



