MO TOR FUNCTIONS OF THORA CICO-L UMBA R UTFL OW 39 



and the motor nerves are necessarily distributed with the skin 

 branches of the spinal nerve corresponding to the particular sym- 

 pathetic ganglion. It may therefore be stated that, in addition 

 to the motor neurons of the vascular system already considered, 

 the ganglia of the main sympathetic chain consist essentially 

 of segmentally arranged motor neurons to a system of involuntary 

 muscles underlying the skin. I will call this system of unstriped 

 muscles under the skin, the dermal system of involuntary muscles ; 

 and therefore conclude from the previous statements that the 

 dermal system of involuntary muscles is exclusively supplied with 

 motor fibres from cells in the vertebral or main chain of sympa- 

 thetic ganglia (Fig. 4). 



4. The motor nerves of muscles surrounding the segmental duct, 

 So far, except incidentally, I have not touched upon the great 

 system of the splanchnic nerves, nerves which constitute the con- 

 nector nerves to the collateral ganglia the superior and inferior 

 mesenteric ganglia, etc. The collateral ganglia have nothing to 

 do with the segmental nerves, but are concerned entirely with the 

 internal visceral organs situated in the abdomen and pelvis. In 

 every case the motor cells to the blood vessels of any organ are 

 found in the ganglion which supplies the organ itself with sym- 

 pathetic nerves. Thus the semilunar ganglion supplies the 

 stomach, liver, and spleen with sympathetic nerves and also the 

 vaso-motor fibres to these organs ; the superior mesenteric ganglion 

 bears the same relation to the small intestine, and the inferior 

 mesenteric to the large, with respect to all sympathetic fibres in- 

 cluding the vaso-motor ones ; the renal ganglion supplies similar 

 fibres to the kidney, and the spermatic or ovarian ganglion to the 

 blood vessels of the testis or ovary respectively. 



We have however not exhausted the nerve cells belonging to 

 the sympathetic system by the consideration of the lateral and 

 collateral ganglia, for some of the medullated fibres of the lumbar 

 splanchnic nerves travel still farther afield before they arrive at 

 their appropriate nerve cells. These cells, which are motor cells, 

 are situated mainly if not entirely close on to the muscles to 

 which they supply motor nerves. This most important muscul- 

 ature, which is exclusively supplied with motor nerves from 

 motor cells connected with the thoracico-lumbar outflow, con- 

 stitutes a morphological system differing somewhat from the 

 vascular and dermal systems already considered, for it consists of 



