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



membrane, which came away when these were separated ; and there was not any ap- 

 pearance of a placental structure, or of villi, or a determination of vessels to this point, 

 on either of the opposed surfaces of the chorion or uterus. The greater part of the 

 membranes of the foetus was collected into a wrinkled mass, which was removable 

 from its position, together with the foetus, by the slightest pressure of the probe. 



The chorion was extremely thin and lacerable ; and upon carefully examining its 

 whole outer surface, no trace of villi or of vessels could be perceived. Detached portions 

 were then placed in the field of a microscope, but without the slightest evidence of 

 vascularity being discernible. The next membrane, whose nature and limits will be 

 presently described, was seen extending from the umbilicus to the inner surface of the 

 chorion, and was highly vascular. The foetus was immediately enveloped in a trans- 

 parent amnios. The four extremities and tail were very obvious, but the toes of 

 the hind legs were not developed. The nostrils were open and proportionately large ; 

 the eyelids were not fully formed, but allowed a little of the eyeball to appear. 

 The tongue projected from the mouth, which, from the imperfect growth of the jaws, 

 appeared more naturally open than in the mammary foetus. The auditory passages 

 were indicated by slight longitudinal depressions, below which the branchial aper- 

 tures, one on either side, each about half a line in length, were very conspicuous. 

 On dilating these apertures two passages were seen leading from each of them to the 

 pharynx. The anterior extremities were well set off from the body, and the five toes 

 on each were very apparent, terminated by minute glistening horny claws. The length 

 of each fore leg was two lines, that of the hind leg only one line, terminated by a flat- 

 tened, undivided, club-shaped mass. The tail was two lines long, thick and strong 

 at the commencement. Impressions of the ribs were visible at the sides of the body. 

 The membranous tube of the spinal marrow was visible along the back between the 

 ununited elements of the vertebral spines. Posterior to the umbilical chord there 

 was a small projecting penis, and behind that, on the same prominence, was the 

 anus, which was pervious. 



The external membrane, or chorion (Plate VII. fig. 1. a.), corresponded in extent 

 with the enlarged cavity formed by the plication of the lining membrane of the 

 uterus which contained the foetus. Its texture in every part was delicate and almost 

 friable ; it was opake and minutely wrinkled. A reiterated examination was made, 

 with a view to discover any trace of a vascular or villous structure, such as exists in 

 the chorion of the Mare and Sow; but the chorion presented in this respect a similar 

 condition with the membrana putaminis or membrana corticalis of the oviparous 

 embryo. 



On turning the chorion away from the foetus, it was found to adhere to the vascu- 

 lar membrane above mentioned, into which the umbilical stem suddenly expanded. 

 With a slight effort, however, the two membranes could be separated from each other 

 without laceration for the extent of an inch ; but at this distance from the umbilicus 

 the chorion gave way on every attempt to detach it from the internal vascular mem- 



