C. THE (ESOPHAGUS, BY E. KLEIN. 531 



close to the muscularis mucosse, which their excretory ducts 

 penetrate obliquely in a downward direction, opening on the 

 surface of the epithelium with a constricted orifice. 



The muscularis externa, or outer muscular coat, is composed 

 in Man of an external longitudinal and an internal circular 

 layer of fibres. The former is arranged in three divisions ;* 

 the middle, and by far the strongest, arising from a triangular 

 elastic membrane attached to the posterior surface of the cricoid 

 cartilage ; the two lateral, which partly descend for a short 

 distance internally to the circular layer of the oesophagus, arise 

 from the elastic bundles in which a portion of the Thyreo- 

 pharyngo-palatinus muscle terminates. The longitudinal fibrous 

 layer in its further course is strengthened by the musculus 

 broncho-oesophageus.t The circular fibrous layer gives off on 

 each side the musculus crico-pharyngeus, and receives accessory 

 fibres in the thoracic cavity from the musculus pleuro-ceso- 

 phageus.J The circular layer continually increases in thickness 

 as it descends, whilst the longitudinal layer, which exceeds 

 the circular layer in thickness in the first fourth, continually 

 diminishes as it descends. 



The external muscular layer is not everywhere of equal 

 thickness ; in adults it is on the average 1'5 to 2 millimeters 

 thick, and, according to Schmauser, is at the upper part more 

 strongly developed on the anterior wall than upon the posterior, 

 then diminishes as it descends upon both surfaces, but espe- 

 cially upon the anterior, until in the lower third it is equally 

 developed throughout the whole circumference of the tube. 



A few smaller fasciculi, both from the internal circular and 

 from the external longitudinal fibrous membrane are given off, 

 which descend vertically, internal to the former, and external 

 to the latter ; the fasciculi are particularly large in the lower 

 fourth, and are derived from the circular layer, becoming verti- 

 cal as they descend. 



The tendons of the fasciculi of the smooth muscular tissue 



* Henle, Splanchnologie, p. 141. 



t Hyrtl, Zettschrift der Gesellschaft der Aerzte zu Wien, 1844, p. 115 ; 

 and Treitz, Prager Vierteljahresschrift, 1853, Band i. 

 t Hyrtl, loc. cit. 

 Schmauser, Dissert, inauguratis, 1866. 



