58 OPHIDIAN EEPTILES. 



cancellated structure at their articular ends. Their lower end 

 supports a short cartilaginous membrane, closing the haemal 

 arch, which is attached to the broad and stiff abdominal scute. 

 These scutes, alternately raised and depressed by muscles attached 

 to the ribs and integuments, aid in the gliding movement of 

 serpents." 



The peculiar motion of Snakes was first noted by Sir Joseph 

 Banks, and commented on by Sir Everard Home. Sir Joseph 

 was observing a Coluber of unusual ske, and thought he saw its 

 ribs come forward in succession, like the feet of a caterpillar. To 

 test this, he placed his hand under the animal, the ends of the ribs 

 were distinctly felt pressing upon the surface in regular succession, 

 leaving no doubt that the ribs formed so many pairs of levers, by 

 means of which it moves its body from place to place. 



The muscles which bring forward these ribs, according to Sir 

 Everard, consists of five sets. One from the transverse process of 

 each vertebra and the rib immediately behind it, which rib is 

 attached to the next vertebra. The next set goes from the 

 rib near the spine, and passes over two ribs, sending a slip to 

 each, and is inserted into a third, a slip connecting it with the 

 next muscle in succession. Under this is ;a third set, issuing 

 from the posterior side of each rib, passing over two ribs, and send- 

 ing a lateral slip to the next muscle, and is also inserted in the 

 third rib behind. And so on throughout the five sets of muscles. 



On the inside of .the chest there is a strong set of muscles 

 attached to the anterior surface of each vertebra, ;and passing 

 obliquely forward over four rit>s is inserted into the fifth one only 

 in the centre. From this part of each rib a strong flat muscle comes 

 forward on each side, before the viscera, forming the abdominal 

 muscles and uniting in a middle tendon, so that the lower half of 

 each rib which is beyond the origin of this muscle, and which is 

 only laterally connected to it by a loose cellular membrane, 

 is external to the belly of the animal, and is used for the pur- 

 pose of progressive motion, while that half of each rib which 

 is next the spine, as far as the lungs extend, is employed in 

 respiration. 



These observations of Sir Everard Home -apply to all Snakes ; 

 but the muscles were compared with a skeleton of the Boa- 



