36 WILLIAM A. LOCY AND OLOF LAESELL 



The traditional view, that somehow the bird's king should be 

 swung into line with the others, and ought to be compared part 

 by part with the mammalian lung, persisted for a long time and 

 created difficulties of interpretation. The idea that there are 

 culs-de-sac on the ultimate twigs of the bronchioles, correspond- 

 ing to the alveoli of the mammalian lung, has so often been 

 tacitly assumed in the descriptions of the anatomy of the bird's 

 lung that confusion has resulted. The conception, so funda- 

 mentally different from this, of labyrinthine passages, all inter- 

 comnmnicating, and forming bronchial circuits instead of a 

 bronchial tree, has been a matter of gradual growth. 



Inasmuch as the pioneer observers examined the bird's lung 

 with great care, by transmitted as well as by reflected light, it is 

 pertinent to inquire to what extent the structure of the bronchial 

 tree was anticipated. 



Rathke's ('28) figures of the embryonic lung of the chick show 

 an attempt to represent the internal anatomy of the lung. In 

 his figure 15 of the seven day stage, the main bronchus is shown 

 with hernia-like growths (entobronchi) coming from it. In one 

 of his five figures of the eleventh day (his fig. 16) he shows the 

 air-sacs and a more profuse branching of the bronchial tree. In 

 his figures 11 and 21 he sketches details of the terminal twigs 

 which he illustrates as ending in grape-like clusters. These he 

 compares directly with the alveoli of the sheep's lung of which he 

 gives a similar picture. 



Von Baer ('28) gives no picture of the embryonic lung but his 

 descriptions show that his observations were carefully made. 

 While Rathke's are tinctured with a subjective bias, Von Baer's 

 are objective. 



The next figures of importance for our review are those of 

 Remak ('55). He was an excellent observer and his sketches are 

 of high quahty. His illustrations show clearly two entobron- 

 chial buds on the fourth day of development (his fig. 78). This 

 shows well the mesenchymic sheath and the endodermal tube. 

 His pictures of the lung at 3^^ days (fig. 72), at the end of the 

 fourth day (fig. 74), and on the fifth day (fig. 75), show two en- 

 tobronchial buds. His sketch of the early sixth day (fig. 88) 



