MO TOR FUNCTIONS OF THORACICO-L UMBAR UTFLO W 45 



nerve cells in the superior and inferior mesenteric ganglia re- 

 spectively, and are connected with the central nervous system by 

 connector fibres in the thoracico-lumbar outflow (Fig. 7). 



There are also muscles of the nature of sphincters at the 

 fore end of the alimentary canal m the so-called pyloric sphincter, 

 separating the pyloric end of the stomach from the intestine, and 

 the cardiac sphincter between the oesophagus and the cardiac end 

 of the stomach. The innervation of this foremost part of the gut 

 has not been so definitely made out as that of the hinder part ; I 

 will consider it later in connexion with the movements of the 

 stomach and oesophagus. 



In my opinion this sphincter system must receive an ex- 

 planation in the past history of the vertebrate. In my book on 

 the origin of vertebrates I have come to the conclusion that 

 the vertebrates arose from the great group of the Appendiculata, 

 i.e. arthropods and worms, and that the neural canal with 

 its peculiar enlargements in the form of the ventricles was 

 originally the alimentary canal of the invertebrate ancestor, the 

 infundibulum being the original oesophagus. As the animal 

 remained upright this necessitated the formation of a new ali- 

 mentary canal on the ventral side of the body. The evidence 

 is strongly in favour of the view that the essential factor in the 

 formation of this new alimentary canal was a respiratory chamber, 

 in which were included a series of respiratory appendages supplied 

 by a group of segmental nerves, which afterwards became the 

 vagus, glosso-pharyngeal and facial group of nerves. I have given 

 reasons for the belief that such a respiratory chamber originally 

 extended close up to the cloacal region of the animal and ulti- 

 mately became connected with the cloaca by a tube. Originally 

 in my opinion there was a short groove situated in the mid- 

 ventral surface of the body between the respiratory chamber and 

 the cloaca. Surrounding this mid-ventral groove, just as in the 

 Trilobites and Apus, were situated a series of appendages not 

 necessarily respiratory, but serially homologous with the respira- 

 tory appendages in the branchial chamber. This groove became 

 converted into a tube which formed the original very short 

 intestine, connecting the respiratory chamber with the cloaca. 

 The muscles of an intestine so formed would be essentially those 

 belonging to the non-respiratory appendages, and supplied there- 

 fore with motor fibres from cells connected with the vagus group 



