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Show 812 DR. J. MURIE ON PHASCOLOMYS PLATYRHINUS. [June 27, sharper-pointed inwardly curved process. The free border of the spine is not thick posteriorly; but it becomes equal to that of P. platyrhinus and almost broader than that of P. wombat at the posterior half of the acromion process. The coracoid process is bent downwards and inwards, as usual in P. wombat; but the groove where the biceps tendon is lodged is in P. latifrons shallower. Towards the neck it rises with a convexity, and with a roughened elongated pit for the insertion of the tendon of the biceps. In the Common Wombat the supra- and infraspinous fossae are very flat; whereas in P. latifrons and, to a lesser extent, in P. platyrhinus they are concave, more especially the infraspinous fossa. The subscapular surface of the bone in Wombat has shallow ridges and furrows, but in the other species these are much more marked. Clavicle.-In the Platyrhine and Common Wombats this bone equally has a double curvature, being by far the stronger and more grooved in the former animal. In the Hairy-nosed Wombat the clavicles are somewhat straighter than in the others. Of about equal length to those of the Common species, they, in consequence of their straightness and also more inward projection of the acromion processes, give an apparently greater breadth of chest to the Hairy-nosed species. Humerus.-The humerus oi P. platyrhinus is 4^j inches leng, of P. latifrons 4^, and in the specimen of P. wombat examined 4 ^ inches. Excepting in the inequality of size, this bone in the first two species is hardly to be distinguished ; but in P. wombat, although bearing a close resemblance to them in general outline, it has nevertheless pointed differences. Its breadth, both in shaft and extremities, is relatively one-third less ; the deltoid ridge is not so prominent; and, moreover, in P. platyrhinus and P. latifrons this has its outer margin rolled backwards so as to give a greater depth behind to that portion of the shaft. The posterior part of the articulating surface of the head of the humerus in the two latter curves considerably backwards, which is not the case in P. wombat, neither has this last such rough processes for the attachment of muscles. In neither of the specimens under consideration was the interspace of the condyles perforated*, as is said occasionally to be the case in P. wombat. Ulna and Radius.-These bones in P. platyrhinus and P. latifrons approach closely to each other, both in the bend of the bones and in the muscular grooves and ridges. The separation distinctive between these two species is one only of size; the ulna of the first, from the olecranon process to the styloid process, is 6", the same measured in the second is 5"*5. The Common Wombat has this bone 5"*8 long, but not at all so broad and strong as in them, neither has it such a deep exterior muscular groove, and its sigmoid notch is also relatively smaller in size. As to the radius, its length bears an analogous proportion to the other bones of the fore limb-in P. platyrhinus 4"*4, in P. latifrons 4"*1, and in P. wombat 4"*2. In the last the shaft is not so strong * Owen, Trans. Zool. Soc. vol. ii. p. 401. |
