MARSUPIALIA. The skulls of the various types of the Marsupials frequently bear a strong superficial resemblance to those of some of the different groups of placental mammals. Thus the skull of the Dasyuridae resembles that of the Carnivora, the resemblance being most marked between the skulls of _Thylacinus_ and the dog. The skull of _Notoryctes_ is strongly suggestive of that of an Insectivore, and that of other Marsupials such as the wombat, recalls equally the characteristic features of a Rodent's skull. But, however much they may differ from one another, the skulls of all Marsupials agree in the following respects. (1) The brain cavity, and especially the cerebral fossa, has a very small comparative size. (2) The nasals are always large, and the mesethmoid is extensively ossified, and terminated by a prominent vertical edge. (3) Processes from the jugal and frontal in living forms never meet and enclose the orbit, but the zygomatic arch is always complete. (4) The jugal always extends back to form part of the glenoid fossa. (5) The lachrymal canal opens either external to or upon the margin of the orbit, and the nasal processes of the premaxillae never quite reach the frontals. (6) The posterior part of the palate is commonly pierced by large oval vacuities. (7) The tympanic is small and never fused to the bones of the cranium. (8) The carotid canal perforates the basisphenoid and not the tympanic bulla. (9) The optic foramen and sphenoidal fissure are confluent. (10) In every case except _Tarsipes_ the angle of the mandible is more or less inflected. The skull of the extinct _Thylacoleo_ differs from that of all other Marsupials in the fact that the postorbital bar is complete. The hyoid is constructed on much the same plan in all Marsupials. It consists of a small basi-hyal, a pair of broad cerato-hyals, and a pair of strong thyro-hyals. The epi-hyals and stylo-hyals are generally unossified. EDENTATA. In Sloths (Bradypodidae) the sutures become early obliterated, the cranial portion of the skull is rather high, and the facial portion very short. The lachrymal is very small, and its canal opens outside the orbit. The zygomatic arch is incomplete, and the jugal (fig. 91, 5) is curiously forked, but in a manner differing in the two genera. The premaxillae are very small,--in _Bradypus_ quite vestigial. The mandible is well developed, the angle being specially marked in _Bradypus_. In _Choloepus_ the symphysial part is drawn out in a somewhat spout-like manner (fig. 91, 6). In both genera the thyro-hyals are ankylosed with the basi-hyal. [Illustration FIG. 91. SKULL OF A TWO-FINGERED SLOTH (_Choloepus didactylus_) × 1/2. (Camb. Mus.) 1. anterior nares. 2. postorbital process of the frontal. 3. coronoid process. 4. angle of the mandible. 5. jugal. 6. spout-like prolongation of the mandible.]