PHYSIOLOGY. 



pipe. This is a tube, made up of little rings, cartilaginous 

 in front, and muscular or fibrous behind ; and is about eight 

 or ten inches in length. It lies immediately on the gullet or 

 Bsophagus t and extends from the larynx to the third vertebra 

 of the back. 1 Here it divides into two branches, called 

 bronchia, one of which goes to the right, the other to the 

 left lobe of the lungs. The right branch divides again into 

 three principle branches, as soon as it enters the lung ; and 

 the left into two ; corresponding to the number of lobes in 

 each lung ; then they subdivide into an innumerable number 

 of small twigs, like the branch of a tree, until they termi- 

 nate in those small cells already mentioned. These cells are 

 about the one hundredth of an inch in diameter, p 



12. The bronchial tubes then, terminate in minute vesi- 

 cles of unequal size, which are of a cylindrical and some- 

 what rounded figure. These vesicles are large enough to be 

 visible to the naked eye, and present something of the ap- 

 pearance of a cluster of currants attached to their stem, as 

 shown in the following cut : 



Fig. 6. 

 View of the Bronchial Tubes, terminating in Air vesicles. 



External view. 1. Bronchial tube. | 

 2. Air vesicles. I 



The Bronchial tube and Air 

 vesicles laid open. 



\It should be borne in mind that the office of respiration is 

 to bring the blood in contact with the airjand, accordingly, 

 the lungs are so constructed as to allow the largest possible 



