OR OSSEOUS SYSTEM. 73 



and of the different parts of the skeleton than we find in 

 fishes ; and many elements originally separate have become 

 anchylosed together, which conditions prepare the solid 

 frame-work to support and carry the whole fabric through a 

 much rarer medium than the dense water in which they 

 commenced their career, and in which the fishes perma- 

 nently reside. 



XXI. Reptilia. The bones of serpents are more com- 

 pact, white, dense, and elastic than those of the other 

 orders of reptiles ; but their skeleton is the most deficient 

 in its parts, consisting almost solely of the vertebral column 

 without legs or arms, or a pelvic or scapular arch, or even 

 a sternum to connect the ribs, as seen in the skeleton of the 

 boa constrictor, (Fig. 3J-) With this simple skeleton they 

 are able to creep quickly on the ground, to combat with 



FIG. 37. 



their prey, to climb trees, to spring into the air, and to swim 

 rivers and lakes. The ribs are developed from the sides of 

 the vertebral column from the atlas to the anus, and the 

 transverse processes continue to extend to a considerable 

 length from the sides of many of the anterior coccygeal 

 vertebrae. From the absence of a sternum in front, and the 

 free articulation of the ribs with the ends of the transverse 

 processes of the vertebrae, the ribs possess the means of 

 extensive motion, and cause the transverse scuta on the 

 lower surface of the abdomen to move like so many feet. 

 The ribs of serpents are tubular, with thin compact parietes, 

 and containing a soft cancellated structure in their interior, 

 by which they possess great elasticity and strength. They 

 are narrow, and compressed from before backwards, strong 

 and broad at their head and neck, and taper regularly to 

 their free ventral extremity, where they generally terminate 



