348 MR. OWEN ON THE GENERATION OF THE MARSUPIAL ANIMALS. 



chus is continued in the same manner from the middle of the anterior part of the 

 bladder, and not from the fundus. 



In neither of the above foetuses of the Kangaroo was there any corresponding 

 trace of umbilical vein, although there was a distinct ligamentum suspensorium he- 

 patis, formed by a duplicature of the peritoneum descending from the diaphragm to 

 the notch lodging the gall-bladder, and not entering, as usual, the fissure to the left 

 of that notch. 



The small intestines in the lesser mammary foetus, when compared with those of the 

 uterine foetus above described, were found to have acquired several additional con- 

 volutions : the fold to which the umbilical vesicle had been attached was still distinct, 

 but now drawn in to the back of the abdomen *. The ceecum was much elongated, 

 but the remaining large intestines proportionately no more developed than in the 

 uterine foetus, resembling those of the Viverrine Camwora ; the subsequent modifica- 

 tion, therefore, of the large intestines seems evidently destined to complete the diges- 

 tion of the vegetable food. 



The stomach was not sacculated, but the division between the cardiac and middle 

 compartments was more marked than in the uterine foetus. Tlje liver had now ascended 

 in its development beyond the oviparous form which it presented in the uterine foetus, 

 the right lobe being subdivided into three. The supra-renal glands bore the same pro- 

 portionate size to the kidneys. The testes were still larger than the kidneys, and were 

 situated below them, not having yet passed out of the abdomen : this takes place when 

 the mammary foetus is about three inches long from the nose to the root of the tail. The 

 ductus arteriosus was distinct in the small mammary foetus, but I could not perceive 

 any trace of the thymus gland. Is this gland unnecessary on account of the preco- 

 cious development of the lungs ? or is its absence connected with the mode in which 

 the foetus in utero is developed ? The latter appears the more probable condition 

 of its absence, as in the oviparous and ovoviviparous classes the thymus gland is 

 rudimental or of doubtful existence. 



Notwithstanding that the new-born Kangaroo 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 Professor GEOFFHovf and Mr. Morgan:}: have shown, is 

 therefore provided with a peculiar adaptation of a muscle (analogous to the cre- 

 master) 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 fcetal efforts of suction should always be coincident with the maternal 



* This process may be compared to that by which the testes are drawn out of the abdomen. 



t M6moires du Museum, torn. xxv. p. 48. + Transactions of the Linnean Society, vol. xvi. p. 61. 



