244. BULLETIN OF THE 
occur. In Enhydra (Sea Otter) the post-tympanic fissure is large ; 
there is also an orbito-nasal deficiency. The infra-orbital opening is 
capacious. 
Uneutata. Artiodactyla. — In many of the Ruminants, as in the Cer- 
vide, Camelide, Antilocapride, and in some of the Bovide, as in Anti- 
lopinze and Caprine, a large facial vacuity exists at the juncture of the 
frontal, lacrymal, malar, and nasal bones, which leads into the nasal 
cavities. (Plate Il. Fig. 8, a.) Where the upper incisors are entirely 
absent, the anterior palatine foramina assume large proportions, becom- 
ing veritable deficiencies. In some of the Cervide, as in Rangifer, 
Alces, and in Antilocapridze, a more or less extensive orbito-nasal vacuity 
exists at the juncture of the vertical plate of the palatine, alisphenoid, 
and lacrymal. In Suidee and Dicotylide the foramen lacerum medium 
is large, and in Hippopotamidze both ante- and post-tympanic foramina 
are capacious. 
Perissodactyla. — In the Equidee, the anterior and posterior tympanic 
foramina with the ovale combine to form an extensive deficiency in the 
postero-lateral basal region. (Plate II. Fig. 9,@.) In the Rhinoce- 
rotide, the foramina, ovale, and lacerwm medium are combined. There 
is also a considerable orbito-nasal vacuity, as well as one formed by 
the combination of the two anterior palatine foramina. 
In Tapiride, the anterior, posterior tympanic foramina, and the ovale 
are joined, as also are the anterior palatine, as in the Rhinocerotide. 
Srrenta.—In the two genera Manatus and Halicore, which consti- 
tute the present order, the entire latero-posterior basal region, between 
the occipital and alisphenoid, may be considered as a vacuity, so imper- 
fectly is it filled by the tympanic and periotic. (Plate II. Fig. 10, a.) 
In the later-ooccipital region, at the juncture of the squamosal with 
the supraoccipital and exoccipital, a large vacuity also exists, very im- 
perfectly filled by the periotic. *(Plate II. Fig. 11, @, 6.) The dilatation 
of the supraorbital foramen is also large, and there are extensive orbito- 
nasal openings. . 
Hyracoimpea. — In Hyrax, the anterior tympanic deficiency is rela- 
tively large. 
ProposcipEA. — In the Elephant, the tympanic deficiencies so uni- 
formly present in the odd-toed Ungulates can scarcely be said to exist. 
Crracea. — In the Odontoceti, and notably in the Delphinoide, large 
irregular openings exist between the recess which holds the united 
tympanic and periotic and the cranial cavity. The optic foramen, as 
it passes out through the orbito-sphenoid, is much enlarged, being 
