196 ANIMAL SKETCHES. CHAP. 



from three different terrestrial genera. Similar adaptations 

 to like conditions have produced the external resemblances. 

 If this be so we have in these sea-snakes another instance of 

 that convergence of superficial characters which is so well 

 seen in the swallows and the swifts. 



For those who admire the delicacies of animal 

 mechanism the skeleton of a snake will exercise some- 

 thing of the fascination which is commonly attributed to the 

 living serpent. The vertebrae of the spinal column are 

 exquisitely fashioned and admirably hinged. Each is 

 articulated with its neighbour by a ball and socket joint 

 below, a wedge fitting into a cavity at the side, and above, 

 on each side, oblique shelves, the even surfaces of which 

 work smoothly on each other. Well may Professor Parker 

 say that in all respects the articulation of the serpent's 

 spine is so exquisitely perfect as to beggar all human 

 invention of joints and hinges, Only just a little motion 

 of joint on joint is allowed, each joint set to the other, so 

 that nothing can part them without crushing them entirely ; 

 and yet there is permitted a most perfect and delicate 

 motion of cup in ball, wedge in wedge and of the oblique 

 overlying facet on the oblique facet beneath it. All 

 these are, moreover, harmonized together, so as just to 

 allow a gentle bend of bone on bone, and a gentle rolling 

 of vertebra on vertebra. Multiply by four hundred this 

 limited motion, this arrested curve of a python's body, and 

 you get a motion such as would, in its sum total, be 

 sufficient to engirdle a luckless anatomist several times 

 over. To the sides of these vertebrae are hinged the 

 ribs. The next time you visit the Zoo, do not fail to 

 notice how the snake walks with his ribs. There is no 

 breast-bone in the snake, but the long and numerous ribs 

 are connected by muscular bands with the broad transverse 

 scales which characterize the belly of the serpent. These 



