PARTS OF ANIMALS, II. ix. 



the region of the heart. The exception is the parts 

 near the belly, which in all animals are boneless. 

 The purpose of this is that the SΛvelling which takes 

 place of necessity after the receipt of nourishment 

 may not be hampered, and (in females) to prevent 

 any interference Avith the groAvth of the fetus. 



The nature of the bones is similar in all viviparous 

 animals (that is, internally viviparous as well as 

 externally) ; and as the \^vipara are much larger 

 proportionately in bodily size than other animals, 

 their bones are strong. In some places many of these 

 animals grow to a great size, as for example in Libya 

 and other hot dry countries. These large animals 

 need stronger and bigger and harder supports, 

 especially those of them that are particularly violent 

 in their habits. Hence, the bones of males are harder 

 than the bones of females, and those of carnivorous 

 animals than those of herbivorous, because the car- 

 nivorous have to fight for their food. An example 

 is the Lion : it has such hard bones that when they 

 are struck fire is kindled as it is from stones. Note 

 that the Dolphin, being viviparous, has bones like the 

 other viviparous creatures, and not fish-spines. 



In the creatures which though blooded are not 

 viviparous Nature has made a series of graduated 

 changes : for example, birds have bones, but they 

 are weaker than the bones of the Vivipara. The 

 oviparous fishes have fish-spine, not bone ; and the 

 serpents have bone whose nature is that of fish-spine ; 

 except the very large species, and they have bones, 

 because (just like the Vivipara) if their bodies are 

 to be strong the solid framcAvork of them must be 

 stronger. The creatures called Selachia " have spines 

 made of cartilage. This is because their movement 



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