46 THE INVOL UNTAR Y NER I/O US S YSTEM 



of nerves. In addition the ventral groove itself may have con- 

 tributed some muscles underlying the ventral skin to the formation 

 of this muscular tube. 



With the subsequent elongation of this new-formed intestine, 

 the respiratory chamber became farther and farther removed 

 from the cloacal region, thus giving rise to the long intestine of 

 the vertebrate, the muscles of which, supplied as they are by the 

 vagus, demonstrate its origin from a prolongation of the respira- 

 tory chamber ; while at the same time a muscular layer under- 

 lying the ventral skin, which, I suggest, helped to form the 

 original short tube, would still remain and form the sphincter 

 system of muscles whose motor nerve cells are situated in the 

 mesenteric ganglia of the sympathetic. 



The whole evidence points to the conclusion that the motor 

 nerve cells, which are connected with the central nervous system 

 by the thoracico-lumbar outflow of connector nerves, supply with 

 motor fibres the whole of the vascular musculature and the whole 

 of a system of unstriped muscles, which originally was lying just 

 under the skin, and also formed the sphincter system in the gut : 

 this latter system may have originated from the dermal mus- 

 culature, but at present we have no direct evidence of such an 

 origin. It conforms to the rest of the dermal musculature, not 

 only in its innervation, but also in its behaviour to the action of 

 adrenalin, thus showing that its characteristics are those of the 

 dermal musculature and not of the neighbouring muscles of the 

 gut. I would suggest therefore the inclusion of the sphincter 

 muscular system under the general title of dermal musculature. 

 Whether the vascular musculature is closely related to the dermal 

 musculature morphologically I am not at present prepared to 

 discuss ; but the close relationship chemically between the two 

 muscular systems is proved beyond doubt by the similar action 

 of adrenalin. 



In order to express in one term the whole of the group of 

 muscles discussed in this chapter, the title " the sympathetic group 

 of muscles " might be used, although it would be better to en- 

 tirely abolish the meaningless term "sympathetic" from verte- 

 brate anatomy. I would suggest as a temporary substitute for 

 the term "sympathetic" the word " vase-dermal" in describing 

 this muscular group, meaning by the term all the vascular muscles 

 and dermal unstriped muscles throughout the body. 



