. On the anatomy of vertebrates [electronic resource] . t of sucking could be , after a gestation of thirty-eight days, is the condition ofthe new-born young of a species of Kangaroo, of which the adult,when standing erect on his hind-feet and tail, can reach to theheight of seven feet. It has greater powers of action than the same sized embryo ofthe sheep ; but less than has the new-born young of the , although it is enabled by the muscular powers of the orbi-cularis oris, and those of the precociously-developed tongue, tograsp and adhere firmly to the nipple, it seems un
. On the anatomy of vertebrates [electronic resource] . t of sucking could be , after a gestation of thirty-eight days, is the condition ofthe new-born young of a species of Kangaroo, of which the adult,when standing erect on his hind-feet and tail, can reach to theheight of seven feet. It has greater powers of action than the same sized embryo ofthe sheep ; but less than has the new-born young of the , although it is enabled by the muscular powers of the orbi-cularis oris, and those of the precociously-developed tongue, tograsp and adhere firmly to the nipple, it seems unable to draw allthe needed sustenance therefrom unaided. And here the modifiedc cremaster comes into play, being adapted to inject the milk intothe small feeble prematurely-born creatures mouth. One cannotsuppose that its efforts at suction should ahvays and exactlycoincide with the mothers act of injection. And we find, infact, provision for the required special relation of the larynx tothe posterior nares. The epiglottis and arytenoid cartilages are. MAMMARY ORGANS IN MARSITIALIA. 773 elongated and approximated, and the rima glottidis is thussituated at the apex of a cone-shaped larynx, fig. 604, c, whichprojects into the posterior nares, where it is closely embraced bythe muscles of the soft palate. The air-passage, b, is thus com-pletely separated from the fauces, and the injected milk passesin a divided stream on either side the larynx to the oesophagus. Thus aided and protected by modifications of structure, bothin the system of the mother and its own, designed with especialreference to each others peculiar condition, and affording, there-fore, the most irrefragable evidence of creative foresight, thesmall offspring of the Kangaroo continues to increase, from sus-tenance exclusively derived from the mother, for a period ofabout eight months. During this period the hind-legs and tailassume a great part of their adult proportions; the muzzle elon-gates; the external ears an
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