658 



MAMMALIA 



[CH. 



,-1 



overlap. Underneath these there are two clavicles and a T-shaped 

 interclavicle, so that the shoulder-girdle recalls the complicated one 

 of the Lizard. 



Ornithorhynchus has webbed feet and lives in the water, feeding 

 on worms and insects, which it digs out of the mud by its broad, 

 shovel-like snout, whence the name Duck-bill (Fig. 325). It crushes 

 its prey by means of horny plates, which are really patches of the 

 hardened gum : when it is young, however, it has true calcareous 

 teeth, two or three on each side of each jaw, but these it loses when 

 it grows older. These teeth are covered by several rows of small 

 points or tubercles. Similar teeth are found amongst the oldest 

 remains of Mammals which are known, the so-called Multituber- 

 culata. 



Echidna lives on ants and other insects, which it ensnares by 



putting out its tongue covered 

 with sticky saliva. Like other 

 ant-eaters it has a long snout 

 and no teeth. It is covered with 

 stiff spines like a porcupine. 



Sub-class II. METATHERIA. 



The division Metatheria in- 

 cludes the curious pouched Mam- 

 mals of Australia and the neigh- 

 bouring islands and the Opossums 

 of America. In these animals 

 the egg is exceedingly small, 

 and the egg-tube is divided into 

 an upper part of correspondingly 

 narrow diameter, called the Fal- 

 lopian tube, and a lower, wider 

 part, called the uterus. In 

 this latter the small egg lies for 

 a while. The egg-shell dis- 

 appears and the egg then de- 

 velops a close adhesion with the 

 wall of the uterus. Through 

 this adhesion nourishment is 

 absorbed and the embryo in con- 

 sequence grows and develops 



FIG. 327. Ventral view of the shoulder- 

 girdle and sternum of a Duckbill, 

 Ornithorhynchus paradoxus x f . 

 After Parker. 



1 and 2. Scapula. 3. Coracoid. 



4. Precoracoid. 5. Glenoid 



cavity. 6. Interclavicle. 7. Clavicle. 

 8. Presternum. 9. Third seg- 

 ment of mesosternum. 10. Sternal 

 rib. 11. Intermediate rib. 12. Ver- 

 tebral rib. 



