. The animals and man; an elementary textbook of zoology and human physiology. Zoology; Physiology. 52 THE ANIMALS AND MAN The skeleton of a backboneless or invertebrate animal differs from that of a backboned or vertebrate animal (as we have seen in comparing the frog and crayfish) not in the use made of it but in its arrangement and in the part of the body from which it is mainly developed. The skeleton of the invertebrate is developed from the skin, and forms a hard casing over the whole or part of the body (fig. i6). It is therefore called an exo-skeleton. In the vertebrates the skeleton i
. The animals and man; an elementary textbook of zoology and human physiology. Zoology; Physiology. 52 THE ANIMALS AND MAN The skeleton of a backboneless or invertebrate animal differs from that of a backboned or vertebrate animal (as we have seen in comparing the frog and crayfish) not in the use made of it but in its arrangement and in the part of the body from which it is mainly developed. The skeleton of the invertebrate is developed from the skin, and forms a hard casing over the whole or part of the body (fig. i6). It is therefore called an exo-skeleton. In the vertebrates the skeleton is mainly developed from tissues within the body and is called in consequence the endo-skeleton. Even more than in the invertebrates it is a system (fig. 17) of levers, fulcra, and points of attachment for muscles to work with, and is as important a part of the Fig. 17. Skeleton of arm organs of motion as is the muscular °^ ™f"' '^''J' ""'f^P" . ,. muscle; to show hosv system itself. bones and muscle act To illustrate the use of the skeleton as levers. (After Jen- of a vertebrate we may examine the "^'"^'^ bones of the hind legs of a cat (fig. 18). The upper bone, the femur, is attached by a joint to the large irregularly shaped bone called the ilium, which is firmly bound to the backbone. Below the femur are two bones, the largest, called tibia, being bound by a joint to the Fig. 18. Skeleton of cat. (After Reighard and femur. Below the Jennings.) tibia is a group of bones, the tarsal bones, pretty firmly fastened together. The largest makes a joint with the tibia. Each of the four tarsal bones toward the toes makes a joint with a. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Kellogg, Vernon L. (Vernon Lyman), 1867-1937; McCracken, Mary Isabel. New York, H. Holt and Compan
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