II.]' 



THE SPINAL SKELETON. 



and Toads we have a middle and xiphoid sternum as also in 

 many Reptiles, and we have all three (as before said) in some 

 Reptiles (e.g. the Crocodile and Chameleon) and in Birds 



The manubrium forms a much larger part of the sternum in 

 some members of man's class than it does in him, as is the case 

 in the Cetacea, the Monotremes, and in the Mole, where its re- 

 lative length about equals that of all the rest of the sternum 



On the other hand, it may be remarkably small and narrow 

 as in the Pig and the Horse. 



FIG. 75. STERNUM OF THE PIG (Sus icrofa). 



/s, manubrium, or pre-sternum ; tits, middle part of the sternum, or meso- 

 sternum ; xs, xiphisternum. 



(From Professor Flower's " Osteology") 



Sometimes this part may develop a strong median keel 

 for muscular attachment, as in Bats, the Mole, and Armadillos. 

 This keel, however, does not answer to the keel of Birds, 

 which belongs to the more post-axial part of the sternum. 



The " episternal granules " occasionally present in man are 

 replaced in some Mammals by considerable horn-like pro- 

 cesses, as in the Howling Monkeys (Mycetes) and Mice. 



The manubrium may be remarkably small when coexisting 

 with a sternum hypertrophied in other parts, as in Birds. 



