THE (ESOPHAGUS. 



501 



II. THE (ESOPHAGUS. 



145. The wall of the oesophagus, 1 J-lf lines thick, consists, exter- 

 nally, of a fibrous membrane composed of connective tissue, with exceed- 

 ingly beautiful elastic fibres. To this succeeds a muscular membrane 

 j-1 line thick, composed of an external, longitudinally fibrous layer, 

 having a thickness of 0-5 of a line, and of an internal, circularly fibrous 

 layer of 0-24-0-3 of a line, which are in close apposition. From the 

 pharynx, where the longitudinal fibres arise in two bundles from the 

 constrictor infimus, united with a third from the cricoid cartilage, they 

 extend as far as the stomach, with whose muscles they are partly con- 

 tinuous. In the upper third of the oesophagus, as far as its entrance into 

 the thorax, transversely striated muscles alone are found, arranged in 

 bundles of 0-04-0-24 of a line, which sometimes distinctly anastomose. 

 Further downwards smooth muscles of the same structure as those in 

 the intestine (infra) make their appearance, in the first place in the cir- 

 cular layer, and subsequently, among the longitudinal fibres ; the pro- 

 Fig. 193. Fig. 199. 



A 



portion of these gradually increases, 

 until at last, in the lower fourth, 

 smooth muscle altogether predomi- 

 nates. Isolated, transversely-stri- 

 ated muscles, however, are, accord- 

 ing to Ficirius, to be met with as far 

 as the cardia. Most internally we 

 find, separated from the muscular 

 coat by a white, soft layer of sub- 

 mucous connective tissue (tunica nervea of the ancients), the pale-red 

 mucous membrane, which below takes on a whitish tint. Its total thick- 



FIG. 198. Transverse section from the middle of the esophagus (Man), magnified 1-2 

 diameters: a, fibrous investment; 6, longitudinal muscles ; e, transverse muscles ; d, tunica 

 nervea ; e, longitudinal muscles of the mucous membrane ; /, papillae ; g, epithelium ; A, aper- 

 ture of a mucous gland ; z, mass of fat. 



Fio. 199. Muscular-fibre cells from the cesophageal mucous membrane of the Pig, after 

 being treated with nitric acid of 20 per cent.; magnified 15 diameters. 



