THE MUSCULAR MOVEMENTS 257 



performed by the brain and its sensory and motor nerves ; the only difEerence being that in the cord the gangUa 

 and its connecting nerves act more or less automatically, whereas in the brain they may and do act voluntarily. Both 

 views are tenable, and there are good grounds for believing that the first arrangement (a) may be traced to the 

 second arrangement (b), where the practically voluntary and independent action of the cord is converted bv the 

 force of habit into mechanical and what are known as reflex acts. Reflex acts are in no sense purposeless. This 

 hypothesis of the double action of the cord is greatly strengthened by the fact that the brain is an expansion of 

 the cord, and because the nerve elements in the cord and the brain are essentially the same. When the spinal cord 

 acts independently of the brain, it does so through its ganglia or nerve centres, which perform the functions of httle 

 brains, and these I have ventured to designate " brainlets." 



Reflex acts are not necessarily confined to the spinal cord. Under certain circumstances they may and do 

 extend to the brain, in which case they are regarded as examples of unconscious cerebration. As it is not possible 

 in a healthy normal animal to separate the spinal cord from the brain, neither is it possible to separate the funda- 

 mental functions of the two. This explains how voluntary muscular actions, frequently repeated and at stated 

 intervals, may become involuntary or automatic actions, as happens in the case of walldng. 



Reflex acts, under ordinary circumstances, can scarcely be said to have an existence as apart from the brain. 

 When an animal is deprived of its head, and co-ordinated and other movements are induced in its limbs through 

 the instrumentality of the cord by artificial stimulation, what one sees are movements stereotyped in the cord due 

 to similar movements occurring originally in the brain, the said movements in the brain being voluntary but 

 rendered involuntary by repetition and habit. Reflex movements derive their value from their original connection 

 with the movements due to the operation of the brain and the nervous system generally. The nervous system in 

 a normal healthy animal acts as a whole. It may, however, under exceptional circumstances act piecemeal or in 

 parts. The brain, for example, is divided into certain areas, which discharge specific functions, and the same is true 

 of the spinal cord up to a point. As the part cannot be taken for the whole, neither can spinal cord reflex acts 

 (which are involuntary and automatic) be regarded as other than secondary to the direct acts of the brain, which 

 are voluntary. The anatomy of the nervous system precludes the separation of the spinal cord from the brain. 

 The nervous system extends to every part of the body, and its branches, plexuses, and ramifications are distributed 

 to all the tissues. 



Where there is no breach of continuity anatomically, it would be a mistake to attempt a separation of 

 function, unless in a general way and on particular points. 



Reflex acts (in the sense explained above) have important uses. They take a leading part in the performance 

 of all those movements which, whatever they may have been originally, have become automatic or mechanical. They, 

 as it wpre, supervise all those acts which are beyond the control of the animal, such as the circulation, respiration, 

 alimentation, the vegetative processes, &c. 



In order fully to understand what is meant by a reflex act in animals it is necessary to say a few words regarding 

 the nervous system in its highest form as witnessed in man. 



Usually the nervous system in man is regarded as consisting of two parts — the cerebro-spinal and sympa- 

 thetic systems ; the former displaying gangha, end-bulbs, connecting nerve-fibres, sensory and motor nerves, nerves 

 of special sense, &c. The latter reveals similar and corresponding nerve elements. The cerebro-spinal system 

 consists of the cerebrum and spinal cord, and these important nerve centres are lodged in bony cavities for protection. 

 The great sympathetic system of nerves consists of a chain of ganglia hnked together by a cord of their own, and 

 placed outside the osseous cavities on either side and in front of the spinal column. 



A further division is attempted, whereby the nervous system is separated into cerebral nerves, cerebro-spinal 

 nerves, spinal nerves, sensory and motor nerves, nerves of special sense, sympathetic nerves, &c. Both divisions 

 are convenient, but they are purely arbitrary, and no physiological conclusions of importance can be founded 

 on them. 



As the ganglia of the brain, spinal cord, and sympathetic systems have much in common, and are united to each 

 other directly and indirectly by commissural nerve fibres, it follows that neither the cerebral, cerebro-spinal, spinal, 

 nor sympathetic systems are complete of themselves. There is, as a matter of fact, structural continuity which 

 forbids functional differentiation. 



The great cerebro-spinal centre which constitutes the chief portion of the nervous system sends its spinal and 

 other nerves to the body in symmetrical pairs. Of these, twelve proceed from the cavity of the cranium through 

 apertures at its base. The next issues from an opening between the occipital and atlas bones. The remaining thirty 

 nerves issue from the sides of the vertebral column, each nerve below the body of a vertebra. 



The distribution of the several kinds of nerves enumerated above is very extensive, and, as was to be expected, 

 not a little involved and obscure. Thus the nerves of the sympathetic system are said to send branches to the 

 VOL. I. ^ ^ 



