DEVELOPMENT OF LUNGS AND BUOYANCY STRUCTURES 



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Fig. 306. Lung development in the chick. (All figures, with the exception of A, were 

 redrawn from Locy and Larsell: '16, Am. J. Anat., vols. 19, 20; A original.) (A) Ex- 

 ternal view of lung rudiment during third day of incubation. (B) Transverse section 

 through pharynx and lung pouches of embryo of 52 to 53 hrs. of incubation. (C) Sec- 

 tion slightly anterior to (B), showing laryngotracheal groove. (D) Lateral view of 

 lung outgrowth of chick at close of fourth day of incubation. (E) Diagram of dissection, 

 exposing left lung of 9-day embryo. Air sacs are now evident; observe relation of heart 

 to lungs. (F) Ventral view of lungs and air sacs of 12-day embryo. (G) Diagram 

 of lateral view of bronchi of 9-day embryo. Four ectobronchi, from which parabronchi 

 are arising, are shown at right of figure. 



b. Lung Development in the Chick 



1) General Features of Lung Development. The development of lungs in 

 the chick differs greatly from that in the Amphibia and other vertebrates. 

 (For a thorough description of the developing lung of the chick, reference 

 should be made to Locy and Larsell, '16, a and b.) 



Lung development begins during the first part of the third day of incubation 

 in the form of ventro-lateral, ridge-like enlargements of the pharynx, imme- 

 diately posterior to the fourth pair of branchial (visceral) pouches. These 

 evaginations arise from a ventral, groove-like trough of the pharyngeal floor 

 (fig. 306A). The entire area of the pharyngeal floor, where the lung rudiments 

 begin to develop, gradually sinks below the pharyngeal-esophageal level, and 

 its remaining connection with the pharynx proper is the laryngotracheal groove 

 in the floor of the pharynx (fig. 306B, C). 



After the lung and tracheal rudiments are formed, they extend backward 



