. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 266 MARSUPIALIA. Leyden Museum, the canines have a longitu- dinal groove on the outer side. The characteristic form of the trenchant pre- molar has just been alluded to : its maximum of development is attained in the arboreal Po- toroos of New Guinea ( Hypsiprymnus ursinus and Hyps, dorcocephalus), in the Tatter of which its antero-posterior extent nearly equals that of the three succeeding molar teeth. In all the Potoroos the trenchant spurious molar is sculp- tured, especially on the outer side, and in young teeth, by
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 266 MARSUPIALIA. Leyden Museum, the canines have a longitu- dinal groove on the outer side. The characteristic form of the trenchant pre- molar has just been alluded to : its maximum of development is attained in the arboreal Po- toroos of New Guinea ( Hypsiprymnus ursinus and Hyps, dorcocephalus), in the Tatter of which its antero-posterior extent nearly equals that of the three succeeding molar teeth. In all the Potoroos the trenchant spurious molar is sculp- tured, especially on the outer side, and in young teeth, by many small vertical grooves. The true molars each present four three-sided pyramidal cusps; but the internal angles of the two opposite cusps are continued into each other across the tooth, forming two angular or concave transverse ridges. In the old animal these cusps and ridges disappear, and the grind- ing surface is worn quite flat, as in Jig. 91, which represents the dentition of the original Potoroo, described in White's Voyage. Genus MACROPUS. Kangaroos. In the genus Macropus (Jig. 92) the normal condition of the permanent teeth may be ex- pressed as follows:— Incisors, 3 — 3 1 — 1 canines 0 — 0 0 — 0 premo- lars, - ; molars, - = 28. 1 — 1 4 — 4 The main difference, as compared with siprymnus, lies in the absence of the upper canines as functional teeth ; the germs, how- ever, of these teeth are always to be found in the young mammary fcetus of the Macropus major, and I have seen them present, but of very small size, and concealed by the gum, in the adults of some small species of kangaroos, Fig. Macropus major, one-third nat. sixe as Macropus rufiventer, Ogilby, and Macr. psdopus, Gould. This, however, is a rare ex- ception ; while the constant presence and con- spicuous size of the canines will always serve to distinguish the Potoroo from the Kangaroo. But there are also other differences in the form and proportions of certain teeth. The upper incis
Size: 2176px × 1148px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bo, booksubjectanatomy, booksubjectphysiology, booksubjectzoology
