DEGLUTITION. 1ST 



left again, and from behind forward, to its opening into the 

 stomach. In its passage through the diaphragm, it is sur- 

 rounded by muscular fibres, so that when this muscle is con- 

 tracted in inspiration, its action has a tendency to close the 

 opening. 



The coats of the oesophagus are two in number, unless 

 we include, as a third coat, the fibrous tissue which attaches 

 the mucous membrane to the subjacent muscular tissue. 



The external coat is composed of an external longitudi- 

 nal, and an internal circular or transverse layer of muscular 

 fibres. In the superior portion, the longitudinal fibres are 

 arranged in three distinct fasciculi : one in front, which passes 

 downward from the posterior surface of the cricoid cartilage ; 

 and one on either side, extending from the inferior constric- 

 tors of the pharynx. As the fibres descend, the fasciculi 

 become less distinct, and are finally blended into a uniform 

 layer. The circular layer is somewhat thinner than the ex- 

 ternal layer. Its fibres are transverse near the superior and 

 inferior extremities of the tube, and are somewhat oblique in 

 the intermediate portion. The muscular coat is fiom ^to 

 y 1 ^ of an inch in thickness. 



In the upper third of the tube, the muscular fibres are ex- 

 clusively of the red or striated variety, with some anastomos- 

 ing bundles ; but lower down, there is a mixture of non-stri- 

 ated fibres, which appear first in the circular layer. These 

 latter fibres become gradually more numerous, until, in the 

 lower fourth, they largely predominate. A few striated 

 fibres, however, are found as low down as the diaphragm. 1 



1 KOLLIKER, Manual of Human Microscopic Anatomy, London, 1864, p. 314. 



Sappey (Traite cT Anatomic Descriptive, Paris, 1857, tome iii., p. 92) makes 

 the extraordinary statement that " the fleshy layer of the oesophagus is formed 

 exclusively of smooth fibres." He says that it is very easy to distinguish the 

 striae of the red fibres with a magnifying power of two-hundred diameters ; and 

 that these are never observed in fibres taken from any part of the oesophagus. It 

 is remarkable that, at the present day, there should be any difference of opinion 

 concerning a question so easily decided as that of the constitution of the muscu- 

 lar coat of the oesophagus. Immediately before writing this paragraph, we had 



