742 MAMMALIA. 
Reptiles and Amphibians) and a T-shaped prosternum 
{sometimes called interclavicle), on which the inner ends of 
the clavicles rest, the outer ends abutting on the acromion 
of the scapule. In Ornithorhynchus the ischia form a long 
ventral symphysis; in Zchidna the acetabulum socket for 
the femur is incompletely ossified (reminding one of Birds, 
though it is only a secondary peculiarity); the pubes bear 
epipubic bones, as in Marsupials. On the side of the 
tarsus, in the duckmole, there is a spur perforated by the 
duct of a gland. This spur is well developed in the males, 
but rudimentary in the females. The male Zchidna has a 
similar but smaller spur. The fibula 
has a proximal process like an ole- 
cranon. 
The brain is smooth in the duck- 
mole, convoluted in £chidna; the 
cerebellum is not covered by the 
cerebrum, there is a large anterior 
commissure, and the corpus cal- 
losum is rudimentary or absent. 
Fic. 403.—Pelvis of The food canal ends in a cloaca. 
iin The right auriculo-ventricular valve 
‘Lo te ee in Ornithorhynchus is partly muscular 
of obturator foramen ag in Birds, while in other Mammals 
between ischium and pubis -, - 
). it is membranous and worked by 
papillary muscles attached to it by 
tendon-like cords (chord tendinez). The temperature 
of the blood is about 25°-28° C., and is noteworthy in 
being unusually variable. In fact, the Monotremes are 
imperfectly warm blooded. 
The ureters open, not into the bladder, but into the 
urogenital canal, as they do in the embryos of higher 
Mammals, 
The testes remain in the abdomen. The left ovary is 
larger than the right, as in Birds. The vasa deferentia 
open separately into the urogenital canal. So in the 
female do the oviducts, and these have no fringed fim- 
briated apertures nor distinct uterine region. The penis is 
attached to the ventral wall of the cloaca, and the uro- 
genital canal communicates both with the cloaca and with 
the canal of the penis. ‘The whole structure resembles in 
