Snakes are highly specialized reptiles. Like that of birds, their body structure seems to have been stripped to the essentials for their way of life. Snake skulls contain many fewer bones than do those of lizards, for example. Snakes have no trace of forelimbs, and only a few of the primitive snakes retain vestiges of the hind limbs.
A Garter Snake
Photo courtesy of the U.S. Fish and Wildlife Service
The loss of nonessential bones and other structures has meant a greater flexibility of the body. While many bones have disappeared, the muscles of the body wall have become differentiated into tiny groups with individual actions. The body muscles of a snake have become more specialized and more highly organized than those of any other animal.
The bones of the skull, except for those of the braincase itself, are very loosely connected to one another, and the jaw muscles have become specialized so that each element can move individually. Thus the entire snake is constructed as a creature of high mobility and flexibility. It has discarded the heavy armor that is characteristic of many lizards, and of reptiles in general, for a body form and structure that allow it maximum strength combined with great agility. Skeleton
The skeleton of a typical snake is made up of the skull and jaws with their associated teeth and a long flexible backbone made up of vertebrae with the associated ribs. There is no sign of a pectoral girdle (for forelimbs) or a breastbone, and only a few snakes have vestiges of the pelvic girdle and the hind limbs. The hyoid is represented by a U-shaped or Y-shaped structure. Backbone and Ribs
The backbone of the snake is made up of many vertebrae -- frequently more than 300. Those vertebrae in the body area are all very much alike. Each has many processes, or projections, for the insertion of muscle slips and a paired process for the attachment of the ribs. A special set of projections on the front and rear of the vertebrae lock adjacent vertebrae together. This arrangement gives the backbone unusual flexibility without the attendant danger that the vertebrae might slip and injure the spinal cord that they enclose.
The ribs are rather simple, single-headed, curved types. One pair is borne by each of the body vertebrae. The ribs do not join below but have free ends. They vary in size but are structurally much alike. However, a few snakes, such as hognose snakes, are able to pull some of their ribs out so as to flatten the body, or, as in the cobras, to form a hood.