OSTEOLOGY OF SERPENTS. 681 



two hundred and fifty-two support ribs : flexibility is therefore abun- 

 dantly provided for in the construction of these lithe and elegant beings, 

 inasmuch as the division of their spinal column into so many pieces 

 allows the utmost pliancy in any required direction. Flexibility, how- 

 ever, is not the only condition requisite in this case : strength and pre- 

 cision of movement are equally indispensable ; and the question is, how 

 are these apparently opposite qualities to be so combined and associated 

 as not in the slightest degree to interfere with each other? The 

 mechanism conspicuous in the construction of the spine of a Serpent is 

 in this respect truly admirable. The anterior extremity of the body of 

 every vertebra is rounded into a smooth and polished ball (fig. 334, c), 



Fig. 334. 



Vertebrae and Eibs of Sou. 



which exactly fits into a hemispherical cup excavated in the substance 

 of the vertebra next succeeding : a perfect ball-and-socket joint is thus 

 formed between every vertebra and that which precedes or follows it ; 

 and thus the spine is rendered capable of the utmost latitude of move- 

 ment, and offers at the same time a firm purchase to the muscles acting 

 upon the vertebral column. To provide, however, against undue extent 

 of motion in certain directions, we now meet with other processes de- 

 rived from the vertebral arches : in addition to those given merely as 

 levers for the attachment of muscles, secondary apophyses, called oblique 

 or articulating processes, become developed; and contiguous vertebrae 

 being likewise moveably connected together by means of these append- 

 ages, unnecessary flexure is not allowed, and all danger of dislocation 

 prevented. 



(1905.) Serpents, being entirely deprived of external limbs, have 

 neither shoulder nor pelvis, their ribs alone affording them the means of 

 progression. These extend on each side in an uninterrupted series from 

 the .first vertebra behind the head to the origin of the tail, so that the 

 division of the spine into regions is here out of the question. Every rib 

 is attached at its origin by a kind of ball-and-socket joint (fig. 334, a, b) 

 to the extremity of the corresponding transverse process of a vertebra, 

 and is therefore freely moveable. There is no sternum here, neither 

 are there sternal ribs ; but the dorsal ribs, wielded as they are by innu- 

 merable and powerful muscles connected with them, literally perform the 

 office of internal legs, and materially assist the creature in progression. 



