422 DR MORRISON WATSON AND MR ALFRED H. YOUNG 
24 inches. Each is flattened from above downwards, and measures 14 inch 
in breadth. They enter the mediastinal surfaces of the respective lungs about 
one-third nearer the apex than the base, and somewhat nearer the dorsal than 
the ventral margin of the latter. As in the trachea, so in the bronchi, the 
cartilaginous rings are complete. The mucous membrane lining the air- 
passages is thrown into longitudinal folds, as in the majority of the larger 
mammalia. 
Lungs.—Each lung measures 18 inches in length from base to apex, and 
presents three uniformly smooth surfaces. Neither of the lungs shows the 
slightest trace of any tendency to lobar subdivision. The surfaces of the lung 
are parietal, mediastinal, and diaphragmatic—names which sufficiently indicate. - 
their relative positions and connections with surrounding parts. <A thick and 
rounded superior border, as well as a thin and sharp inferior margin, are 
noticeable. Each principal bronchus enters the inner or mediastinal surface 
of the corresponding lung, as previously described; the single or accessory 
bronchus reaches the inner surface of the right lung, and enters its substance 
midway between the point of entrance of the principal bronchus and the apex. 
Upon the left side the principal bronchus, after entering the lung, furnishes 
a large offset, which runs forward towards the apex, whilst the main tube 
continues backward to the base of the organ, lying close to its mediastinal 
surface and superior border. Erom these primary tubes secondary branches 
pass off in all directions, except towards the inner surface of the lung. The 
subdivision of the bronchial tubes within the lung does not take place dicho- 
tomously, as in Balenoptera Sibbaldui,* but is quite irregular. The carti- 
laginous elements of the intra-pulmonic bronchi are in the form of complete 
rings, even where the latter do net exceed -/;th of an inch in diameter. This 
recalls to mind the similar arrangement met with in the lungs of the Dugong.t 
Water injected into the main bronchus of the right lung does not distend 
the apex of this organ, which, indeed, can only be effected when the fluid is 
introduced through the medium of the accessory bronchus. From this circum- 
stance, it appears that in Beluga the communication between the principal and 
accessory bronchi of the right lung is not so free as Hunter { affirms it to be 
in other species. This relation, however, according to JAcKson,§ is not so 
common as HUNTER imagined. 
The pleural membrane covering the lung is thick and leathery, but we could 
not distinguish any subjacent elastic coat such as is found in many of the larger 
mammals, 
Lying in close relation to the inferior border of each lung, and near the 
junction of its diaphragmatic and inner surfaces, is a large lymphatic gland, 
* XVII. p. 235. ¢ XXI. vol. iii, p. 580. { XVI. p. 334, § IV. 149. 
