508 OPHIDIANS. 



around the head, and is pushed off gradually, being turned inside 

 out, like the finger of a glove. This rejection of the slough 

 was to many of the ancients, a sign of a renovated state of ex- 

 istence ; they regarded these reptiles as leading a protracted life 

 of annually renewed vigor and beauty. The internal frame- 

 work or skeleton of serpents is extremely simple, consisting of 

 the skull, the vertebral column, and the ribs, (Plate XII. fig. 5.) 

 The breast bone is wanting; so also are the bones of the hips, 

 and of the limbs, excepting where the hind pair exist in the form 

 of hook-like stylets, as in the Boas. A reference to the plate of 

 the skeleton just referred to, must satisfy any one of its elegance, 

 and also suggest the idea of its flexibility, which an examination 

 of its parts will fully confirm. 



The vertebral column consists of a series of bones united to 

 each other by beautiful ball-and-socket joints ; the head of each 

 separate vertebra being received into a deep cup-like cavity of 

 the one succeeding it. The whole of the spine is, in reality, a 

 chain of these joints, firmly locked together, each movable to 

 such extent as is consistent with the safety of the spinal cord. 



Serpents are capable of twisting themselves in the most extra- 

 ordinary manner; but their pliability consists less in the mobil- 

 ity of each joint separately, however great this be, than in the 

 number of joints into which the vertebral column is divided. 

 Two ribs, one on either side, arise from each of the distinct 

 bones of that column. Its bones are exceedingly numerous, 

 being always more than a hundred, and in some species amount- 

 ing to more than three hundred. 



The ribs, forming a large portion of a circle, embrace nearly 

 the whole circumference of the body; and to these reptiles are 

 the efficient agents of locomotion. They each severally play on 

 a convex protuberance of the respective vertebrae, and are acted 

 upon by powerful muscles, which move them backwards and 

 forwards. Instead of being attached at their extremity to a 

 breast bone, as is the case in the Mammals and Lizards, each 

 pair, by means of a slender cartilage, is connected with one of 

 the scuta, or shield-like plates of the under surface. The ribs 

 may be likened to the limbs of the millipede or thousand-legged 

 worm ; they support the weight of the snake, and in its progres- 

 sion, work like the legs of that insect. 



Although destitute of limbs, yet some serpents are capable 

 of rapid advances. On the" surface of the ground, their pro- 

 gression is made in two ways. The ordinary movement, when 

 the body is straightened out entirely in contact with the ground, 

 is by a succession of short steps, taken by the numerous ribs, as 



