394 STRUCTURE OF THE (ESOPHAGUS. [BOOK n. 



sometimes spoken of as a fibrous sheath. In, or rather perhaps on, 

 this sheath in the lower part of the oesophagus run the two vagi 

 nerves, with the oesophageal plexus which is formed by branches 

 running from the one to the other. In it also run the larger 

 blood vessels. 



223. It is obvious that the oesophagus is much more a 

 muscular than a secreting structure, and further that a distinction 

 is to be made between the upper part of the oesophagus where the 

 muscular fibres are striated, and the lower part where they are 

 unstriated. Corresponding more or less clearly to this distinction 

 we find that though the whole oesophagus is supplied by nerve 

 fibres from the trunk of the vagus (which however it must be 

 remembered contains besides fibres of the vagus proper, fibres from 

 the spinal accessory nerve and from other sources) the supply to 

 the upper part takes a different course from the supply to the 

 lower part. Thus in man the upper part is supplied by branches 

 of the recurrent laryngeal nerve as it runs up between the trachea 

 and oesophagus, while the lower part derives its nerve fibres from 

 the oesophageal plexus formed by the two vagi. In various 

 animals the supply of the upper part varies, coming in some cases 

 chieHy from the pharyngeal branch of the vagus, and being in the 

 rabbit a distinct branch of the vagus. In all cases however it 

 would seem that the lower part of the oesophagus, the upper limit 

 being placed higher or lower in different animals, is supplied from 

 i lie oesophageal plexus. It may be remarked that the fibres in 

 this plexus are for the most part non-medullated fibres, but we 

 shall have to return to these nerves in speaking of the movements 

 of the oesophagus. 



