394 



ON RESPIRATION. 



Fig. 97. cesophageal tube. In the chick, about 



the fourth day, a little sacculus is de- 

 scribed as shooting forth at its posterior 

 and inferior part ; and this soon sub- 

 divides at its lower part into two, at the 

 same time becoming more separated 

 from the tube by a constriction around 

 the neck, which soon elongates so as to 

 form the trachea. On the fifth or sixth 

 day, the lung of one side is completely 

 distinct from that of the other, and each 

 is attached to the common pedicle by 

 a peculiar branch, the future bronchus. The upper portion has much thicker 

 walls than the lower, and these appear to contain a large quantity of vesicular 

 parenchyma, in which the ramifications of the bronchial tubes subsequently 

 extend themselves. About the tenth or eleventh day of incubation, these rami- 

 fications possess nearly their permanent character and situation. The first 

 trace of the glottis appears about the fifth day ; it is then a mere slit in the 

 walls of the ossophagus, resembling that by which the ductus pneumaticus of 

 some fishes opens into the alimentary canal. The formation of the cartilaginous 



[Fig. 98. 



First appearance of the Lungs ; a, in a Fowl at 

 four days ; b, in a Fowl at six days; c. termination 

 of bronchus in very young Pig. (After Rathke.) 



The Larynx, Trachea and Bronchiae, deprived of their fibrous covering, and with the outline of the 

 Lungs; 1, 1, outline of the upper lobes of the lungs; 2, outline of the middle lobe of the right lung; 3, 3, 

 outline of the inferior lobes of both lungs; 4, outline of the ninth dorsal vertebra, showing its relation to 

 the lungs and the vertebral column; 5, thyroid cartilage; 6, cricoid cartilage; 7, trachea; 8, right bronchus; 

 9, left bronchus; 10, crico-thyroid ligament; 11, 12, rings of the trachea; 13, first ring of the trachea; 14, 

 1 ast ring of the trachea, which is corset-shaped; 15, 16, a complete bronchial cartilaginous ring; 17, one 

 which is bifurcated; 18, double bifurcated bronchial rings; 19, 19, smaller bronchial rings; 20, depressions 

 for the course of the large blood-vessels.] 



