MAMMALIA 



347 



that, generally speaking, they are much less specialized than are 

 either the ungulates or the whales. Even Man, apart from his re- 

 markable brain and his upright position, is a comparatively unspe- 

 cialized mammal. If this disrespectful treatment of lordly Man shocks 

 the gentle reader, let him remember that several authorities have 

 already assigned to the birds the distinction of being the most highly 

 specialized vertebrate class; so the edge is taken off the contest for 

 first honors in the second division. 



' SUB-CLASS I. PROTOTHERIA (MONOTREMATA, EGG-LAYING) 



MAMMALS 



The modern representatives of this sub-class are few, consisting of 

 but three genera of strange beasts native to Australasia. Some frag- 



FIG. 181. Pectoral arch and sternum of Ornithorhynchus anatinus. c' 1 c 2 , c 3 , 

 first, second and third ribs; cl, clavicle; ec, epicoracoid; e$ l and es 2 , prosternum 

 (episternum) m. c, metacoracoid (coracoid) ; ra. s, manubrium sterni; sc, scapula; 

 st, sternebra. (From Wiedersheim.) 



mentary remains of Multituberculata, already discussed in the sec- 

 tion dealing with the Mesozoic mammals, have also been assigned by 

 some authorities to this division. 



The Monotremata are mammals that lay large eggs with a shell, 

 abundant yolk, and albumen (eggs practically reptilian in character) ; 

 they have diffuse mammary glands without teats; the brain lacks the 

 corpus caliosum; the shoulder girdle has a large coracoid (Fig. 181) 

 reaching to the sternum; an interclavicle is present; paired marsupial 



