MAMMALIA. 717 



In the mammary fetus of a Kangaroo a fortnight old, Profes- 

 sor Owen detected both an urachus and umbilical arteries, but 

 these only extended from the bladder and iliac vessels as far as the 

 umbilicus ; neither could any umbilical vein be found penetrating 

 the liver. It is in the placental Mammals that we shall find 

 these vessels assuming their full importance, and developing them- 

 selves into a new system, whereby the communication between the 

 mother and her offspring is still more effectually provided for. 



(845.) When we consider the very early period at which the 

 young Kangaroo is born, namely, at about the thirty-ninth day 

 after conception, it is only reasonable to suppose that the organs most 

 immediately connected with the vital actions are precociously ma- 

 tured ; and accordingly, even in the embryo above delineated (fig. 

 330), the intestines, the liver, the kidneys, and the testes were all 

 conspicuous, and the diaphragm, the heart, and the lungs were in 

 such an advanced condition as to show that they would soon be 

 capable of prematurely taking upon themselves the exercise of the 

 circulatory and respiratory functions. 



(846.) This rapid developement of the viscera connected with 

 circulation and respiration, is in truth essentially requisite ; for no 

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

 figure (Jig. 331, A), and while the limbs are still in a most rudi- 

 mentary condition, 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 

 obtained, until it has acquired sufficient strength and size to leave 

 the strange portable nest in which its fetal growth is accomplished, 

 and procure food adapted to a maturer condition. 



(847.) A very beautiful provision is met with in the construc- 

 tion of the respiratory passages of the young Marsupial, intended 

 to obviate the possibility of suffocation consequent upon the admis- 

 sion 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 re- 

 ferred 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 sus- 



* Page 348. 



