In the anterior part of both jaws the teeth are simple, conical, or slightly compressed, and sharp pointed. The first three in the upper jaw are distinctly implanted in the premaxillary bone, and so may be reckoned as incisors. The tooth which succeeds, or the canine, is also simple and conical, but it does not exceed the others in size. This is followed by five teeth having two distinct roots and compressed pointed crowns, with denticulated cutting-edges. The dentition is therefore _i_ ³⁄₃, _c_ ¹⁄₁, _p_ and _m_ ⁵⁄₅ = 36, resembling that of some Seals.[139] General form of the skull elongated and much depressed. Brain-cavity very small, and the skull between it and the orbits elongated and narrow. Temporal fossæ very large. A strong sagittal crest. Rostrum long and narrow, differing from that of other Cetaceans in the large extent to which the premaxillæ form the sides of the anterior extremity. Nasal bones elongated, flat, and narrow, the opening of the anterior nares being over the middle of the elongated compressed rostrum. All the cervical vertebræ free. The characters of the dorsal vertebræ and mode of articulation of the ribs appear to have resembled those of _Platanista_ rather than _Balæna_, _Physeter_, or _Delphinus_. Lumbar vertebræ with elongated bodies, low neural spines, and the transverse processes placed low down on the bodies. Characters of the limbs not known with certainty.[140] All the known fossil remains belonging to the animals of this group may be referred, provisionally at least, to the genus _Zeuglodon_, so named because the first section of a molar tooth examined was taken from the base of the crown, where it was beginning to divide into the two roots, and looked like two single teeth “linked or yoked together.” This name was substituted by Owen for the earlier one _Basilosaurus_ of Harlan, with the consent of that author, on the mammalian nature of the animal being demonstrated.[141] The latter name is, however, still generally retained by American zoologists. The remains have hitherto been found chiefly in the Eocene formations of the States of Alabama, Louisiana, Mississippi, and Arkansas, and have been assigned to several species. A portion of a skull is recorded from the Barton Clay (Eocene) of Hampshire, England. _Suborder_ ODONTOCETI, _the_ DELPHINOIDEA, _or Toothed Whales_.