MONOTREMATA. 



401 



to be granted to it in order to direct its move- 

 ments. The privation of this sense, on the 

 contrary, implies a confinement to the nest, 

 and a reception on land of the mammary 

 secretion of the parent. 



The auditory orifices (fig. 196, d) are situated 

 about a line behind the eyes. 



The general form of the body and the carti- 

 laginous condition of the bones of the extre- 

 mities equally militate against the young Orni- 

 thorhynchus possessing, at this period of its 

 existence, active powers of swimming or creep- 

 ing. The head and tail are closely approxi- 

 mated on the ventral aspect, requiring force to 

 pull the body out into a straight line ; and the 

 relative quantity of integument on the back and 

 belly shows that the position necessary for the 

 due progressive motions is unnatural at this 

 stage of growth. 



The toes on each of the four feet were com- 

 pletely formed, and terminated by curved, co- 

 nical, horny claws ; but the natatory fold of 

 membrane of the fore foot had not the same 

 proportional extent as in the adult, and the 

 spur of the hind foot did not project beyond its 

 socket in either specimen. In the smaller one, 

 which was a male, it presented the form of an 

 obtuse papilla; while in the larger specimen, 

 although a female, it was more plainly developed 

 and more pointed (fig. 197, f). This circum- 



Fig. 197. 



Hind-foot and spur, young female Ornithorhynchus, 

 magnified. ( Owen, Zonl. Trans. ) 



stance is inexact accordance with the known laws 

 of the development of sexual distinctions, espe- 

 cially of those of secondary importance, such 

 as beards, manes, plumes, horns, tusks, spurs, 

 &c., which do not avail in distinguishing the 

 sexes till towards the period of puberty. As 

 the spur is the only obvious distinction of the 

 sexes in the full-grown Ornithorhynchus, I 

 was compelled to refer to the internal essential 

 organs, in order to determine the sex of the 

 specimens here described. 



The ventral surface of the smaller specimen 

 was carefully examined with a lens ; but no 

 trace of an umbilicus could be satisfactorily 

 determined. In the very young or newly born 

 Kangaroo, a longitudinal linear trace of the 

 attachment of the umbilical vesicle is at that 

 time apparent, but it is rapidly obliterated ; 

 as is probably also the case in the Ornitho- 

 rhynchus. 



In the smaller specimen the intromittent 

 organ projected a little way beyond the excre- 



VOL. III. 



mentory orifice, as in the young Marsupial ia ; 

 but it was not continuous, as in them, with the 

 anterior margin of that outlet. In the larger 

 female specimen the corresponding organ was 

 visible just within the verge of the opening ; 

 but this clitoris, remaining stationary in its 

 development, is afterwards, as I have shown in 

 my paper on the Mammary Glands of the Mo- 

 notremes,* removed to a distance from the 

 preputial aperture by the elongation of the 

 sheath, just as the minute spur of the female 

 lies concealed at the bottom of the progres- 

 sively elongated tegumentary socket, and as 

 the tongue is left at the back of the oral cavity 

 by the growth of the jaws. 



The following anatomical appearances were 

 noticed in these young Ornithoihynchi: 



On laying open the abdomen in the larger 

 specimen, the most prominent viscus was the 

 stomach, which was almost as large as in the 

 adult animal, deriving at this period no assist- 

 ance from the preparatory digestive cavities, 

 the cheek-pouches, which were not yet deve- 

 loped. The stomach extended in a curved 

 direction across the epigastric and down the 

 left hypochondriac region to the left iliac re- 

 gion. It was full of coagulated milk. 



In the smaller specimen the stomach was 

 empty; when distended with air it exhibited 

 a less disproportionate development. It was 

 situated in the left hypochondriac and lumbar 

 regions. The intestines contained air, with 

 granular masses of a mucous chyme adhering 

 to their internal surface. This condition of 

 the digestive canal would seem to show that 

 no long period had elapsed since the birth of 

 the specimen, and that either lactation had not 

 been in full action, or that the young one had 

 been deserted by the parent for some time 

 before it was taken. 



In both specimens the spleen bore a propor- 

 tionate size with the stomach ; and as the dif- 

 ference in the development of the stomach was 

 considerable, the correspondence between the 

 condition of the spleen with that of the diges- 

 tive cavity was made very obvious. 



The difference in the development of the 

 liver was not greater than corresponded with 

 the different size and age of the two specimens. 

 But the pancreas in both bore the same ratio to 

 the stomach as the spleen. This,therefore,would 

 seem to afford some indication of the organs 

 with which the function of the spleen is more 

 immediately related. 



The intestinal canal in the larger specimen 

 was situated almost entirely on the right side 

 of the abdomen. The ca-cnm in both was very 

 minute and filamentary. I examined the ileum, 

 and more especially in the usual situation above 

 the caecum, but could not perceive any trace of 

 the pedicle of the umbilical or vitelline vesicle. 

 The other vestiges of foetal organization were 

 more obvious than in the ordinary marsupial 

 or ovoviviparous Mammalia. 



In both specimens, but more especially in 

 the smaller one, the umbilical vein was seen, 

 extending from a linear cicatrix of the perito- 



* Phil. Trans, for 1832, p. 525. 



2 D 



