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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 

XI. Splanchnology
 
  UNDER this heading are included the respiratory, digestive, and urogenital organs, and the ductless glands.
 
1. The Respiratory Apparatus
 
  
(Apparatus Respiratorius; Respiratory System)


The respiratory apparatus consists of the larynx, trachea, bronchi, lungs, and pleuræ.


FIG. 947– The head and neck of a human embryo thirty-two days old, seen from the ventral surface. The floor of the mouth and pharynx have been removed. (His.) (See enlarged image)


Development.—The rudiment of the respiratory organs appears as a median longitudinal groove in the ventral wall of the pharynx. The groove deepens and its lips fuse to form a septum which grows from below upward and converts the groove into a tube, the laryngo-tracheal tube (Fig. 947), the cephalic end of which opens into the pharynx by a slit-like aperture formed by the persistent anterior part of the groove. The tube is lined by entoderm from which the epithelial lining of the respiratory tract is developed. The cephalic part of the tube becomes the larynx, and its next succeeding part the trachea, while from its caudal end two lateral outgrowths, the right and left lung buds, arise, and from them the bronchi and lungs are developed. The first rudiment of the larynx consists of two arytenoid swellings, which appear, one on either side of the cephalic end of the laryngo-tracheal groove, and are continuous in front of the groove with a transverse ridge (furcula of His) which lies between the ventral ends of the third branchial arches and from which the epiglottis is subsequently developed (Figs. 980, 981). After the separation of the trachea from the esophagus the arytenoid swellings come

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