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Show 1892.] POSITION OF NOTORYCTES TYPHLOPS. 365 the Marsupials, Notoryctes, and the Monotremes, and is morphologically the same through which runs the urine in the male Monotremes. II. The shoulder-girdle of Notoryctes is built after the Marsupial type ; it shows the complete absence of an interclavicle, of coracoids, and of " epicoracoids." As confirmatory evidence of the affinities of Notoryctes with the Monotremes, Mr. Ogilby mentions "the considerable development of the clavicle, which is connected by ligament to the sternal apparatus, along with the rudimentary character of the epipubic bones being also Monotrematous." The clavicles of Notoryctes are weak, their slenderness of function is obviously indicated by their long ligamentous connexion with the manubrium sterni. In the Dasyures and in the Bandicoots the clavicles are very rudimentary or even absent, while in the Monotremes they are, by means of a large interclavicle, fastened to the sternum as firmly as possible. " It may be sought to explain away this difference in the strength of the shoulder-girdle on the grounds that Notoryctes, Echidna, and Ornithorhynchus have the fore limbs strengthened in order to enable them to burrow with the greater ease ; but the superficiality of such a view is demonstrable at a glance, if we take into consideration the fact that the Peramelidce, which are also of fossorial habits, though not in so marked a degree as the genera mentioned above, are absolutely without rudiments of these bones." This may be, but the composition of the shoulder-girdle and sternal apparatus of Notoryctes is one of the strongest proofs against its Monotreme affinities. Its ancestors had lost the very strength of the sterno-scapular and humeral support which is so essential to an intensely fossorial animal, and its organism has resorted to a new device of giving strength to the chest by an extraordinary development of the first pair of ribs. The latter firmly fix the anterior portion of the sternum and secure the development and working of strong pectoral and humeral muscles. A similar case is afforded by the Dasypodidce. Is it more likely that a burrowing, digging creature like an Echidna would give up its strongly secured chest, or that a Marsupial (which as such had lost coracoids and interclavicle, and obeys the general law that parts once lost by reduction cannot be redeveloped) which assumes strongly fossorial habits would resort to strengthening some of those parts which it does possess, namely ribs, in order to attain a similar result 1 H o w the rudimentary character of the epipubic or marsupial bones of Notoryctes can be used as evidence of its affinity to Monotremes is not obvious, considering that in both Echidna and Ornithorhynchus these bones are much stronger and larger than in any Marsupial. III. The marsupium seems to be a permanent organ in the female Notoryctes, and a pair of minute mammary prominences, devoid of hair and ending in nipple-like projections, have been discovered by Professor Stirling. This is likewise a Marsupial, not a Monotrematous character. The pouch in Notoryctes opens backwards towards PROC. ZOOL. Soc-1892, No. XXVI. 26 |
