CATALOGUE 



MONOTREMATA. 



MONOTEEMATA. 



Tekeesteial or aquatic Mammals, bringing forth their yoivig ovi- 

 parously, and nourishing them after their exit from the egg with a 

 lacteal fluid expressed from the mammary glands into a temporary 

 abdominal pouch. The ducts of these glands do not open upon the 

 summits of projecting mammse, but merely upon the surface of the 

 bottom of the pouch, into which the head of the young is inserted 

 and retained. The oviducts open separately into a cloaca, to which 

 there is but a single external orifice for the passage both of the 

 fsecal and reproductive elements. The muzzle is produced forwards 

 into a beak, either flattened or cylindrical. The opening of the 

 external ear is without a conch. The limbs are subequal in length, 

 short and powerful, and are modified in one of the two families 

 into swimming-paddles. In both families the male possesses a per- 

 forated horny spur on the inner side of the heel, supported on a 

 special ossicle attached partly or whoUy to the distal end of the 

 tibia. The spur is connected by a duct with a gland situated at 

 the back of the thigh. The tail is either short and broad, or rudi- 

 mentary. ' 



In the skeleton clavicles, large and functional coracoids, epicora- 

 coids, and epipubic bones are present in both families, and, in 

 addition, there is a large T-shaped interclavicle, a bone without 

 any homologue in other Mammals. 



The skull has a large, smoothly rounded cranial portion and a 

 long muzzle modified to support the horny beak. The zygomata 

 are complete. The bony palate is much produced backwards, the 

 posterior nares being about on a level with the middle of the cranial 



