34 MAMMALIAN DESCENT. [Lect. II. 



small coracoidal snag or beak (or imperfect coracoid), as 

 in Man and most mammals, but the lower or ventral 

 part of the girdle is continued downwards to articulate 

 with the sternum (or breast-bone) as a large and perfect 

 coracoid. Here we have a condition like that wdiich is 

 seen in Amphibia and Sauropsida (Reptiles and Birds) ; 

 on the other hand, the aljortive development of the 

 coracoid, and the freedom of the shoulder-girdle from the 

 sternum, is a true diagnostic of a high Mammalian. 



The scapula (or blade-bone) in the Prototheria is very- 

 primitive in its form, being falcate, or scythe-shaped, and 

 having a very low spine ; the coracoid is continued from 

 it to the sternum as a large flat bone, and the fore part 

 of the crescentic base of the whole plate is ossified as a 

 separate epicoracoid, a part well seen in the Frog and 

 Lizard. Such a term as "epicoracoid" for the more or 

 less distinct broad part of a coracoid is not needed in 

 mammals generally, for in them the lower part of the 

 arch is absent, although it reappears in the native Bat 

 and Shrew. In birds the whole of the main coracoid 

 bar is ossified from one bony centre. Here, again, the 

 Monotremes have to be compared with types below the 

 bird class. 



Now it is well known that one diagnostic of the 

 mammal is that it has only a pair of cla^dcles, or collar- 

 bones, and that these are not simple parostoses or splints, 

 but compound bones, composed of cartilage above and 

 below, and of ossified fibrous tissue in the middle. But 



