PYTHONID&. 53 



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 form 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, consist 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 sending 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 ribs, 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 purpose 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 Constrictor in 

 the Hunterian Museum, which is thirteen feet nine inches in length. 

 The habit of attaching themselves to trees, and holding on by the 

 tail, their heads and bodies floating listlessly over some sedgy river, 

 is explained by the structure of the tail. Dr. Meyer has minutely 

 described the manner in which they hook themselves to a tree, which 

 gives them the power of a double fulcrum. The apparatus which 

 gives this power is a spur or nail on each side of the vent in the 

 Pythonidcz, in which the anatomist discovered the elements of an 

 unguinal phalanx articulated with another bone much stronger, which 

 is concealed under the skin. 



Following the arrangement of the Pythonida adopted by 

 Dr. J. E. Gray we find : 



I. Morelia, having a strong prehensile tail, distinct head, truncate 



