68 ELEMENTAR Y ANA TOMY. [LESS. 



having many ribs indeed, Fishes few or many, and Che- 

 lonians few, but all having no sternum, so that every rib 

 must be reckoned to be a false rib in them and this in spite 

 of their fixity in Tortoises. 



In the proportion of true to false ribs man occupies an 

 intermediate position. Thus the number of true ribs is more 

 in excess in some other animals than in him, as e.g. in the 

 Seals, and in Birds ; yet the number of false ribs is greatly 

 in excess in some other animals, especially in the Whalebone 

 Whales, in which there may be but one pair of true ribs. 



In the shape of the ribs man is normal, and their length 

 always exceeds their breadth or thickness. They may, how- 

 ever, be vastly thicker or more massive than in him, as is 

 the case in the Manatee, or habitually form thickenings which 

 but for their constancy would be deemed a diseased condition 

 (pathological), as in the fish Platax. 



They may also greatly exceed the breadth possessed by 

 man's, as in the Two-toed Ant-eater, where they overlap one 

 another ; they may, on the contrary, be less flattened than in 

 him, as in the Carnivora. 



As to the number of pairs of ribs, this has already been 

 generally indicated in speaking of the dorsal vertebras, though 

 in Birds we may have ribs coming from vertebras which are 

 generally counted as " sacral." There may be as few as five 

 or six pairs, as in Ampkiuma, or the number may reach 320, 

 as in some Pythons. In man's class there may be as many 

 as twenty-four pairs, as in the Two-toed Sloth, or as few as 

 nine, as in the Hyperoodon. 



In the fact that ribs (distinct and articulated) are confined 

 to the dorsal region, man agrees with most Vertebrates. Such 

 ribs, however (more or less free and more or less long), may 

 exist in the cervical region, as we see in the Crocodile and in 

 many Reptiles ; in the so-called " sacral" region, as we see in 

 Birds ; and even in the caudal regions, as we see in Meno- 

 branchus. Of such ribs, however, enough has been said in 

 treating of those regions of the spine. 



The function of aiding respiration is one which the ribs 

 possess in the higher Vertebrata, but quite other purposes 

 may be subserved by them in addition to, or instead of, 

 respiratory action. Thus ,'certain ribs, by excessive elonga- 

 tion, may support a flying membrane, as in the Flying Dragon, 

 or by their sudden erection expand the skin of the neck, as 

 in the Cobra. 



Terrestrial locomotion may also be due to these parts, as in 



