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 nib, 
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 
describéd the manner in which they hook themselves toa 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 
Pythonide, 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 /Pythonide adopted by 
Dr. J. E. Gray in the catalogue of the British Museum, we find :— 
~~ 
I.— Morelia, having a strong prehensile tail, distinct head. truncate 
