I 
THORACIC VISCERA OF SOME LARGE MAMMAL 97 
A. THE TRACHEA, BRONCHI, AND LUNGS. 1 
Inflate the lungs by means of a large blowpipe inserted through 
the trachea and guarded by a compressible rubber tube as a 
mouthpiece, which may be pinched together to prevent air 
returning from the lungs to your own respiratory passages. 
Note that each lung has a large posterior lobe and a smaller 
bilobed anterior one and that the right lung has an additional 
lobe which fits into the space posterior to the heart. 
With the dorsal surface of the material uppermost, expose the 
trachea by removing the oesophagus and turning the aorta forward, 
start at the anterior end and follow the trachea until it divides 
into the bronchi which enter the various lobes of the lung. By 
removing the lymph glands, fat, and areolar tissue from the 
surface of the bronchi and the pulmonary veins and arteries which 
accompany them into the various lobes of the lungs, the whole 
plan of the air and blood supply to the lungs may be worked out. 
The blood vessels should also be traced in the opposite direction 
to demonstrate their relation to the heart. Note that the pul¬ 
monary veins of the various lobes enter the left auricle of the 
heart, the thin dorsal wall of which is immediately ventral to the 
large bronchi. Show by diagram the whole plan of air and blood 
supply to the lungs. 
In a single posterior lobe trace out by teasing and tearing the 
soft tissues, the entire course of the bronchus and its branches, 
together with the course of the corresponding veins and arteries. 
Note that the arteries are anterior and lateral to the corresponding 
bronchial tubes, while the veins are medial and posterior to them. 
Draw this dissection. 
Note that the smaller bronchial tubes, as well as the bronchi 
and trachea, contain in their walls incomplete rings of cartilage, 
which, while insuring a constantly open condition of the lumen, 
allow at the same time a considerable range of variation in caliber, 
which complete rings would prevent. In the smaller tubes the 
rings become very irregular, and the ultimate branches, the bron¬ 
chioles, possess no cartilage. These, like the alveoli into which 
they lead, are too minute for demonstration by gross dissection. 
1 Keep the material in cold storage (or on ice) in wet wrappings at least until the 
study of the lungs is completed. 
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