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Show 1896.] ZOOLOGICAL EXPEDITION TO MADAGASCAR. 977 developed in H. liberiensls, whilst in H. amphiblus and the H. major of the Upper Pliocene the cranial portion is much reduced, the facial portion on the contrary enormously produced. In connection with this is the great elongation of the frontal bones of H. liberiensls, whilst they are broad and short in H. amphiblus and H. major. H. sivalensis is still very near H. liberiensls in respect, the antero-posterior extension of the frontal being, as was shown by Falconer and Cautley, twice as great as in H. amphiblus. An expression of the relative proportion between the anterior and posterior portions of the cranium is given by the position of the orbits. The various Hippopotamus crania from Madagascar have, in this respect, much resemblance with II. sivalensls, the cranial portion being, however, somewhat more shortened, the facial portion somewhat more lengthened; so that the orbit occupies a less central position than in H. liberiensls, and, as a matter of course, still less so than in H. sivalensls. The Malagasy forms thus constitute a step farther in the direction of H. amphiblus, the breadth of the intraorbital region being much less than in the African species and the same as in H. sivalensls. These changes are reflected by the position which the lachrymal occupies. In H. liberiensls, as shown by Leidy, who had at his disposal the skull of a younger animal, exhibiting distinctly all the sutures, the lachrymal is entirely separated from the nasals by the anterior prolongation of the frontal, which last thus comes in contact with the maxillary. This is, with the exception of the Ruminants, almost the rule in Ungulates. As to II. sivalensls, six out of seven skulls figured in the ' Fauna Antiqua Sivalensis' the sutures are distinctly to be seen ; and we find here again the lachrymal excluded by the frontal from contact wdth tbe nasal and joining the maxillary. The originals of most of the skulls figured being in the National Museum, I have had an opportunity of verifying the accurateness of the drawings, so that we may fairly conclude that H. sivalensis had, as a rule, the character mentioned above in common with H. liberiensls. The same is the case with regard to H. palcelndlcus, as shown in the F. A. S., with the slight difference that the anterior tongue of the frontal is somewhat shortened. In the Malagasy Hippopotami we find, as a rule, the following relations in this part of the skull. The lachrymal departs from the orbital margin in an inward direction and reaches the nasal, with which it unites, thus shutting out tbe frontal from a connection with the maxillary. Anteriorly to the lachrymal, exactly corresponding to the place which in H. liberiensls and H. sivalensls occupied by the foremost tongue of the frontal, we find here a separate bone of various dimensions, interposed between the nasal and lachrymal, and touching the maxillary in front and sometimes the malar bone as well. In II. amphiblus the lachrymal is usually broadly interposed between the frontal and maxillary; but in young specimens we meet occasionally with the same supra-numerary bone; sometimes, as in H. liberiensls and H. sivalensis, 63* |