Epipubic or marsupial bones are present in both sexes of nearly all species. In one genus alone, _Thylacinus_, they are not ossified. The number of dorso-lumbar vertebræ is always nineteen, although there are some apparent exceptions caused by the last lumbar being modified into a sacral vertebra. The number of pairs of ribs is nearly always thirteen. The tympanic bone remains permanently distinct. The carotid canal perforates the basisphenoid. The lachrymal foramen is situated upon or external to the anterior margin of the orbit, and there are generally large vacuities in the bony palate. The angle of the mandible is (except in _Tarsipes_) more or less inflected. The hyoid bones have always a peculiar form, consisting of a small, more or less lozenge-shaped basihyal, broad ceratohyals, with the remainder of the anterior arch usually unossified, and stout, somewhat compressed thyrohyals. There are two anterior venæ cavæ,[38] into each of which a “vena azygos” enters. In the male the testes are always contained in a scrotum, which is suspended by a narrow pedicle to the abdomen in front of the penis. The vasa deferentia open into a complete and continuous urethra, which is also the passage by which the urine escapes from the bladder, and is perfectly distinct from the passage for the fæces, although the anus and the termination of the urethro-sexual canal are embraced by the same sphincter muscle. The glans is often bifurcated anteriorly. In the female the oviducts never unite to form a common cavity or uterus, but open separately into the vagina, which at least for part of its course is double. The mammæ vary much in number, but are always abdominal in position, having long teats, and in most of the species are more or less enclosed in a fold of the integument forming a pouch or marsupium, though in some this is entirely wanting, and the newly-born, blind, naked, and helpless young, attached by their mouths to the teat, are merely concealed and protected by the hairy covering of the mother’s abdomen. In this stage of their existence they are fed by milk injected into their stomach by the contraction of the muscles covering the mammary gland, the respiratory organs being modified temporarily, much as they are permanently in the Cetacea—the elongated upper part of the larynx projecting into the posterior nares, and so maintaining a free communication between the lungs and the external surface independently of the mouth and gullet, thus averting the danger of suffocation while the milk is passing down the latter passage. [Illustration: FIG. 35.—Front view of skull of _Sarcophilus ursinus_, showing polyprotodont and carnivorous dentition (_Quart. Journ. Geol. Soc._ vol xxiv. p. 313).]