MO TOR FUNCTIONS OF THORA CICO-L UMBAR O UTFLO W 43 



hibitory to the circular and vice versa. This law does not hold 

 good for the uterus or the ureters or the vas deferens, for it has 

 been shown conclusively that both motor and inhibitory fibres 

 for the musculature of all these organs arise from nerve cells 

 belonging to the lumbar outflow, there being no evidence that 

 they are connected in the slightest degree with the pelvic 

 nerve. The nerve cells with which they are connected form 

 small groups on the course of the hypogastric nerves either near 

 or in the organs themselves, as is seen in the isolated ganglia 

 near the uterus and in the ganglia along the ureters, as Proto- 

 popow has shown. 



The observations of Langley and Anderson prove clearly that 

 all the motor neurons to the musculature surrounding the Wolf- 

 fian and Miillerian ducts are connected with the central nervous 

 system exclusively by connector nerves in the thoracico-lumbar 

 outflow (Fig. 8). Further, according to Keith, these ducts are 

 epiblast formations, and indeed the segmental duct, from which 

 they are both derived, is in the opinion of many morphologists 

 derived from the epiblast and not from the mesoblast. If this 

 is the case then this musculature belongs to the system of skin 

 musculature and its innervation is yet another proof that the 

 motor nerve cells belonging to the thoracico-lumbar outflow, i.e. 

 the sympathetic nerve cells, are par excellence the nerve cells 

 which supply motor fibres to a very extensive system of unstriped 

 muscles always lying just under the skin. As this system of 

 muscles is especially connected with the internal genital organs 

 and urinary ducts, I will call it the uro-genito-dennal system to 

 distinguish it from the dermal system already considered. 



5. The motor nerves of the sphincter system of gut muscles. 

 So far I have shown that the connector thoracico-lumbar nerves 

 connect with the motor neurons of three distinct systems of 

 involuntary muscles, the vascular, dermal, and urogenito-dermal 

 systems. There is yet another system to be considered, whose 

 motor cells belong to the sympathetic, and which forms a distinct 

 portion of the musculature of the gut. 



The intestinal part of the gut is divisible into two portions, 

 the small intestine and the large intestine or cloacal region. 

 The motor nerve supply to these two portions is very striking and 

 suggestive, for, as will be discussed more fully in the next chapter, 

 the motor cells and nerves for the small intestine are connected 



