338 MR. OWEN ON THE GENERATION OP THE MARSUPIAL ANIMALS. 



The liver consisted of two equal and symmetrically disposed lobes. The vena 

 port£e was formed by the union of the vitelline with the mesenteric and doubtless the 

 other usual veins, which were, however, too small to be distinctly perceived. The 

 diaphragm was very perfectly formed. 



The vena cava inferior was joined, above the diaphragm, by the left superior cava, 

 just at its termination in a large right auricle. The ventricles of the heart were 

 completely joined together, and bore the same proportions to each other as in the 

 adult ; a perfection of structure which is not observed in the embryos of ordinary 

 Mammalia at a corresponding period of development. The pulmonary artery and 

 aorta were of nearly the same proportionate size as in the adult : the branches given 

 off by the former to the lungs were of considerable size. The ductus arteriosus, on 

 the contrary, was remarkably small. The aorta, prior to forming the descending 

 trunk, dilated into a bulb, from which the carotid and subclavian arteries were 

 given off. This bulb, which is permanent in Fish and perennibranchiate Reptiles, is 

 always a prominent structure in the earlier stages of the embryonic heart in pulmo- 

 niferous Vertehrata. I was unable to trace the branchial arteries so satisfactorily as 

 the conspicuous nature of the external openings had led me to expect, owing to the 

 long maceration of the specimen. 



The lungs were of equal size with the heart, being about a line in length, and 

 nearly the same in breadth : they were of a spongy texture, and of a red colour, like 

 the veins, from the quantity of blood they contained. This precocious development 

 of the thoracic viscera is an evident provision for the early or premature exercise of 

 the lungs as respiratory organs in this animal ; and on account of the simple con- 

 dition of the alimentary canal, the chest exceeds the abdomen in size. 



The kidneys had the same form and situation as in the adult. The supra-renal 

 glands were half the size of the kidneys. 



The testes were situated below the kidneys, and were one half larger than those 

 glands, the superiority of size depending on their large epididymis. They continue 

 within the abdomen for six weeks after uterine birth. 



There was no perceptible trace of an allantois, nor even of an urinary bladder, in 

 this foetus =*. 



With respect to the largely developed umbilical vesicle, as it had been laid open 

 before the parts were immersed in spirit, the nature of its contents could not be ascer- 

 tained ; but the quantity of what must be supposed to have been nutritious material 

 had evidently been abundant. As the affinity of the Marsupiata to the oviparous 

 Vertehrata has been believed to be manifested more particularly in the development 

 of the ovum and ovisac, or corpus luteum, it may not be superfluous to offer a few 

 observations on the differences observable in this respect between Mammalia and 



* I have subsequently detected the remains of a urachus and of umbilical or vesical arteries in a mammary 

 foetus of a Kangaroo about a fortnight old, and of a urachus in very small mammary foetuses of a Petaurus 

 pygmceus and of a Phalangista. 



