228 MR. R. OWEN ON THE YOUNG OF THE ORNITHORHYNCHUS PARADOXUS. 
Meckel!. 
The ductus arteriosus was here very evident, and formed a filamentary chord 
in the usual situation between the aorta and pulmonary artery, but proportionately 
longer than in the true viviparous Mammalia. Here also we have the indication of 
a more prolonged foetal existence than in the Marsupial animals, there being no trace 
of a ductus arteriosus either in the uterine or mammary foetus of the Kangaroo. 
The Ornithorhynchus also deviates from the ordinary Marsupiata in having the thymus 
gland. This is situated in front of the great vessels of the heart, and consists of two 
lobes, of which the right is the largest. 
Fig. 
Fig. 
kwh 
@ 
PLATE XXXII. 
The smaller specimen of Ornithorhynchus paradoaus. 
The larger specimen. 
. The same in another view. 
. Front view of the mandibles of the same, a little open to show the tongue. 
In each of these figures, a, is the nostrils ; b, the prominence on the upper 
beak ; c, the eyes; d, the ears; e, the vent ; f, the orifice and rudimentary 
spur of the hind foot; g, the membrane at the base of the mandibles ; 
h, the tongue. 
A magnified figure of the hind foot of the female, showing the rudimentary 
spur projecting from the socket. 
PLATE XXXIII. 
Abdominal viscera of the smaller specimen, principally to show the remains 
of g, the umbilical vein, and h, the allantois ; i, is the liver ; k, the stomach. 
The stomach ; and 1, the spleen of the same specimen, 
The stomach and spleen of the larger specimen. 
. The heart, showing the single ductus arteriosus. 
. m, The kidneys ; n, the supra-renal glands ; 0, the testes; and p, the urinary 
bladder of the younger specimen. 
. The corresponding parts in situ of the female specimen: q, the ovaries; 7, the 
uteri and oviducts. 
. The urinary bladder, umbilical arteries, and allantois (h) of the smaller spe- 
cimen, magnified. 
. The upper mandible of the smaller specimen, magnified, to show the caruncle 
(6) between the nostrils. The figure marked thus * is of the natural size. 
[All the figures, except where otherwise indicated, are of the natural size. Those in Plate XXXII. were 
drawn by my friend T. Rymer Jones, Esq., whose valuable assistance I am happy in acknowledging. ] 
' Ornithorhynchi paradoxi Anatomia, tal. vii. fig. 1. 
