CHAPTER II. 



THE CHARACTERISTIC MOTOR FUNCTIONS OF THE NERVE CELLS 

 BELONGING TO THE THORACICO-LUMBAR OUTFLOW OF CON- 

 NECTOR NERVES ; USUALLY CALLED THE SYMPATHETIC NERVE 

 CELLS. 



I COME now to the question of the functions of the motor neurons 

 belonging to the three outflows cranial, thoracico-lumbar, and 

 sacral. Have they all similar functions or are they clearly dif- 

 ferentiated from each other? I propose in the first instance to 

 confine myself entirely to the consideration of those cells which 

 supply motor nerves to the various kinds of involuntary muscle, 

 and to leave entirely to a later discussion the question of nerve 

 cells which supply inhibitory nerve fibres to muscular structures, 

 or fibres causing secretion of glands. In the present chapter 

 I will consider in the first place the motor neurons connected 

 with the thoracico-lumbar connector nerves (Fig. 4). The result 

 is very instructive, for the evidence shows that: (i) the motor 

 nerves for the muscles of the blood vessels over the whole body 

 belong to this system ; (2) the motor nerves for the musculature 

 of the sweat glands over the whole body belong to this system ; 

 (3) the motor nerves for all unstriped muscle under the skin, 

 whether pilo-motor or not, belong to this system ; (4) the motor 

 nerves for all unstriped muscle in connexion with structures de- 

 rived from the segmental duct belong to this system (Fig. 8). In 

 other words, the essential function of the neurons of the sym- 

 pathetic system, so far as motor nerves are concerned, is to supply 

 such nerves to a layer of unstriped muscle under the skin, 

 around the blood vessels and around the tubular structures de- 

 rived from the segmental duct. A further system also exists, 

 namely (5) the motor nerves to the sphincters of the intestine 

 (Fig. 7), but I will defer consideration of this system to the end of 

 this chapter. I will now consider the first four groups one by one. 

 i . The motor nerves to the blood vessels and to the heart. Two 



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