In the Horse and its allies (Equidae) the facial portion of the skull is very large as compared with the cranial portion, the nasals and nasal cavities being specially large. In the living species of the genus _Equus_ there is no fossa between the maxillae and lachrymal, but it occurs in some extinct species. The lachrymal and jugal form a considerable part of the side of the face; and the orbit though small is complete and prominent. The postorbital bar is formed by a strong outgrowth from the frontal, which unites with a forward extension of the squamosal. The squamosal may extend forwards and form part of the wall of the orbit, a very unusual feature, as in most mammals the squamosal stops before the postorbital bar. The palate is narrow and excavated behind as in _Rhinoceros_; the palatines take very little part in its formation. The glenoid surface for the articulation of the mandible is very wide. The squamosal gives rise to small postglenoid and post-tympanic processes, and the exoccipital to a large paroccipital process. The tympanic and periotic are ankylosed together, but not to any other bones. In the SUBUNGULATA, the lachrymal and jugal do not form any considerable part of the side of the face, and the maxillae commonly takes part in the formation of the zygomatic arch. _TOXODONTIA._ The skull in the Toxodontia shows several Artiodactyloid features, while the manus and pes are of a more Perissodactyloid type. The Artiodactyloid features are (1) the absence of an alisphenoid canal, (2) the fact that the palate is not excavated behind, and that the palatines form a considerable part of it, and (3) the fusion of the tympanic to the squamosal and exoccipital, forming the floor of an upwardly directed auditory meatus. The frontal has a fairly well developed postorbital process, but the orbit is confluent with the temporal fossa. The premaxillae is well developed, as is the paroccipital process of the exoccipital, especially in _Typotherium_. The mandible has a rounded angle and a coronoid process of moderate size. In _Typotherium_ the ascending portion is very massive. _CONDYLARTHRA._ As far as is known the skull of these generalised Ungulates is depressed, and is frequently marked by a strong sagittal crest. The cranial cavity is small, the cerebral fossa in _Phenacodus_ being exceptionally small. The orbit is completely confluent with the temporal fossa.