ON THE ANATOMY OF THE NORTHERN BELUGA. 419 
veloped to a greater extent, would completely separate the two halves from each 
other, and cause them to communicate by distinct apertures with the interior 
of the larynx in precisely the same manner as the ventricles do in the majority 
of mammals. 
We must either accept this view with regard to the homologies of the 
laryngeal sacs of the toothed whales, or regard them as structures altogether 
confmed to the cetacea, and having no representatives in other mammals. 
The latter alternative we are by no means inclined to accept. Nor will it do 
to regard the sacs as homologous with the subepiglottic ventricle of the horse 
and ass, or with the large air space found in a corresponding position in certain 
of the quadrumana (Mandrill*), for the reason that the latter have no relation 
to the thyro-arytenoid muscles, which, in the animals referred to, maintain 
their normal relation to the ventricles of Morgagni, these ventricles occupy- 
ing their usual position in the laryngeal cavity. A similar argument might be 
advanced with reference to the air sac which in Ateles projects outward between 
the thyroid and cricoid cartilages, and which, therefore, at first sight, presents 
an arrangement not unlike that of the large laryngeal sac of the whalebone 
whales. We are, therefore, by a process of exclusion, compelled to regard the 
laryngeal pouches of the toothed whales as homologous with the ventricles of 
Morgagni. Now, if we imagine these pouches (which communicate freely with 
one another by reason of the deficiency of the mesial septum) of the toothed 
whales to be inflated so that the single sac would project altogether beyond the 
space bounded by the laryngeal cartilages, by means of the interval between 
the cricoid and thyroid cartilages, we should have an arrangement essentially 
similar to that of the laryngeal sac in the whalebone whales. In connection 
with this difference in size and relations of the laryngeal sac in the whalebone, 
as contrasted with the toothed whales, it is interesting to observe the adaptive 
modification of the laryngeal cartilages in the latter. The cricoid cartilage in 
these is deficient inferiorly, and the neck or constricted portion of the enormous 
laryngeal sac is supported by the posterior cornua of the arytenoid cartilages ; 
whereas in the toothed whales the cricoid is either complete or almost complete 
inferiorly, and the arytenoid cartilages are destitute of the peculiar posterior 
cornua which in the whalebone whales appear to supply the place of the 
deficient cricoid. Moreover, in the whalebone group the inferior angle of the 
thyroid cartilage is reduced to a mere tongue-like process, so that a large 
interval exists between its posterior extremity and the first complete tracheal 
ring, which interval permits of the passage outwards of the laryngeal pouch. 
In the toothed whales, on the contrary, the thyroid cartilage is not aborted in 
this manner, and the laryngeal pouch does not extend beyond the cavity of the 
* XXXIL plate vii. figs, 1, 2, and 3. 
