FCETAL KANGAKOO. 



829 



- 418t 



Foetal Kangaroo. 



has the embryo arrived at the size represented in the next figure 



(fig. 418, A), the limbs being still in a most rudimentary condition, 



than the embryo is transferred from the uterus into the marsupial 



pouch, where it is found attached by its 



mouth to one of the nipples, from whence 



the materials of its support are to be ob- 



tained until it has acquired sufficient 



strength and size to leave the strange 



portable nest in which its foetal growth 



is accomplished and procure food adapted 



to a maturer condition. 



(2452.) A very beautiful provision is 

 met with in the construction of the respi- 

 ratory passages of the young Marsupial, 

 intended to obviate the possibility of suf- 

 focation consequent upon the admission of 

 milk into the trachea a circumstance that, 

 without some peculiar arrangement, might 

 easily happen ; but of this we must quote 

 the original description, extracted from the 

 paper already referred to *. " The new-born Kangaroo," observes 

 Professor Owen, " possesses greater powers of action than the same- 

 sized embryo of a Sheep, and approximates more nearly in this respect 

 to the new-born young of the Rat ; yet it is evidently inferior to the 

 latter. For although it is enabled by the muscular power of its lips to 

 grasp and adhere firmly to the nipple, it seems to be unable to draw 

 sustenance therefrom by its own unaided efforts. The mother, as Pro- 

 fessor Geoffrey f and Mr. Morgan J have shown, is therefore provided 

 with a peculiar adaptation of a muscle (analogous to the cremaster) 

 to the mammary gland, for the evident purpose of injecting the milk 

 from the nipple into the mouth of the adherent foetus. Now it can 

 scarcely be supposed that the foetal efforts of suction should always be 

 coincident with the maternal act of injection ; and if at any time this 

 should not be the case, a fatal accident might happen from the milk 

 being forcibly injected into the larynx. Professor Geoffrey first de- 

 scribed the modification by which this purpose is effected; and Mr. 

 Hunter appears to have foreseen the necessity for such a structure, for 

 he has dissected two small foetuses of the Kangaroo for the especial 

 purpose of showing the relation of the larynx to the posterior nares . 



* P.Z.S., August 1837, p. 348. f Memoires du Musee, torn. xxv. p. 48. 



J Trans. Linn. Soc. vol. xvi. p. 61. 



"See Nos. 3731, 3734, 3735, in the Physiological Series of the Hunterian Mu- 

 seum, in which there are evidences that Mr. Hunter had anticipated most of the 

 anatomical discoveries which have subsequently been made upon the embryo of the 

 Kangaroo." 



