A TRANSPORT SYSTEM 



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oesophagus carries its load onwards. We are to see that 

 it is a strange form of pump — a pipe-pump, making a 

 wave of contraction which creeps along its muscular wall 

 to serve the purposes of a piston. In our illustration part 

 of the oesophagus has been cut open in order to show a 

 bolus in transit. We have to deal with a muscular tube, 

 9 or 10 inches in length, lined by a loosely attached 

 membrane. The muscular tissue is arranged in two 

 layers or strata ; in the outer layer the spindles are 

 arranged in threads or bundles running along the tube 



A.(Selaxed) ^.(Contracted) 



"Wave of Contraction "Wave of Relaxation 



Lining membrane 



Coat with lubricating glands Longitudinal muscle 



coat 



Fig. 38. — A segment cut out from the oesophagus and laid open to show a bolus 

 in transit. A, a small fragment of the outer muscular coat magnified to show 

 the individual spindle-shaped fibres of which it is composed in a relaxed 

 state. B, fibres or spindles greatly enlarged to show a contracted state. 



lengthwise ; in the inner layer the fibres are arranged 

 circularly, so as to form ring-shaped muscular engines. 

 In fig. 38 a small fragment of the outer muscular coat has 

 been magnified so that the individual spindles of which 

 it is made up may be seen. Certain spindle engines 

 have been greatly enlarged by the artist to show the 

 change of shape when in action and when relaxed. No 

 attempt has been made to depict the rich network of nerve 

 fibres with which the muscular coats of the oesophagus 

 is provided ; by means of this network the myriads of 

 muscle spindles of the oesophagus are harmonised in 

 their work. From the network, nerve paths lead to and 



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