244 BULLETIN OF THE 



occur. In Enhydra (Sea Otter) the post-tympanic fissure is larg-? ; 

 there is also an orbito-nasal deficiency. The infra-orbital opening is 

 capacious. 



Ungulata. Artiodactyla. — In many of the Ruminants, as in the Cer- 

 vidse, CamelidtTe, Antilocapridse, and in some of the Bovidse, as in Anti- 

 lopinae and Caprinse, a large facial vacuity exists at the juncture of the 

 frontal, lacrymal, malar, and nasal bones, which leads into the nasal 

 cavities. (Plate II. 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 Cervidae, as in Rangifer, 

 Alces, and in Antilocapridse, a more or less extensive orbitonasal vacuity 

 exists at the juncture of the vertical plate of the palatine, alisphenoid, 

 and lacrymal. In Suidse and Dicotylidse the foramen lacerum viedium 

 is large, and in Hippopotamidae both ante- and post-tympanic foramina 

 are capacious. 



Perissodactyla. — In the Equidse, 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, a .) In the Rhinoce- 

 rotidse, the foramina, ovale, and lacerum 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 Tapiridse, the anterior, posterior tympanic foramina, and the ovale 

 are joined, as also are the anterior palatine, as in the Rhinocerotidse. 



SiRENiA. — 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, a, b.) The dilatation 

 of the supraorbital foramen is also large, and there are extensive ^orbito- 

 nasal openings. 



Hyracoidea. — In Hyrax, the anterior tympanic deficiency is rela- 

 tively large. 



Proboscidea. — In the Elephant, the tympanic deficiencies so uni- 

 formly present in the odd-toed Ungulates can scarcely be said to exist. 



Cetacea. — In the Odontoceti, and notably in the Delphinoidse, 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 orbitosphenoid, is much enlarged, being 



