SPLANCHNOLOGY. 



TNDER this heading are included the respiratory, digestive, and urogenital 

 ^ organs, and the ductless glands. 



THE RESPIRATORY APPARATUS (APPARATUS RESPIRATORIUS ; 

 RESPIRATORY SYSTEM). 



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

 pleurae. 



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 con- 

 verts the groove into a tube, the laryngo-tracheal tube (Fig. 947), the cephalic 



Mmith of olfactory pit 



Median part of fronto- 

 nasal process 



Processus globulari 



Hypophysis 

 1st branchial pouch 



Sinus cervicalis 



Laryngo-tracheal tube 



Lung 



Maxillary process 



Mandibular arch 



Future tympanic 

 membrane 



Hyoid arch 

 Third arch 



Fourth arch 



io. 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.) 



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 epithe- 

 lial 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 



( 1071 ) 



