374 HUMAN PHYSIOLOGY 



supported as well as carried, the bones are bound more firmly to 

 the axial skeleton. The bones of the foot are so arranged that a 

 springy arch is formed which aids greatly in locomotion. 



Pelvic Girdle and Leg. Laboratory Exercise. — The lower end of the 

 vertebral column in man, as in the frog, is united with a number of broad 

 bones which together form the pelvic girdle. Notice the difference in the 

 shape and position of the pelvic girdle in the frog and in man. In man, 

 the pelvic bones support the organs of the body cavity; this is a peculiar 

 adaptation to the upright position of man. Compare the bones of the hind 

 leg of the frog with those of the human skeleton. Beginning with the large 

 bones next the pelvic girdle, these bones are : the thigh bone, or femur; 

 the shank bones, or tibia and fibula (the tibia and fibula are united into one 

 bone in the frog; the tibia is the larger bone in man; it is on the side of 

 the big toe); the ankle bones, or tarsals; foot bones, or metatarsals; and 

 the bones of the toe, phalanges, so-called from the arrangement which is 

 somewhat like a Greek phalanx of soldiers. Compare the relative size, 

 shape, and number of the bones of the foot and ankle in the frog and in man. 

 Can you explain the differences which occur as an adaptation to the life 

 which the animal leads ? 



Bones of the Pectoral Girdle and Arm. — -Compare the attachment of the 

 fore limb of the frog with that of man. The bones which attach the fore 

 limb to the axial skeleton collectively form the pectoral girdle. Find in 

 the frog the fiat shoulder blade (not quite homologous with the shoulder 

 blade or scapula of man). The collar bone or clavicle is not plainly seen 

 in the frog; note its position in the human skeleton. (See page 372.) Now 

 compare the bones of the fore limb of a frog and in man. The large stout 

 bone of the upper arm is the humerus; the two bones of the forearm (united 

 in the frog) are the ulna and radius; the latter is on the thumb side of the 

 arm. The bones of the wrist are known as car pals; those of the palm of 

 the hand, metacarpals ; those of the fingers, the phalanges. 



Notice how the fore limb of a frog is shortened. The thumb is almost 

 completely lost. Is this an adaptation to the frog's mode of life ? Give 

 reasons. 



Comparison of the Skull of the Frog with that of Man. — Notice the differ- 

 ence in the general shape of the head and the lack of a neck in the frog. 

 In man, two groups of bones make up the skull, the bones of the face and 

 those of the brain case or cranium. In the frog, this distinction is not so 

 easily seen. Notice the upper and lower jawbones in man. Do they 

 bear teeth ? Do you find corresponding bones that bear teeth in the frog ? 

 Are both jaws moved in talking or chewing? Notice how much larger, 

 relatively, the cranium in man is than that of the frog. Notice in man 

 that the bones of the cranium are dovetailed together, such joints being 

 known as sutures. 



The Human Skull. — In man, the cranium is a box made up of eight 

 bones. This is adapted to protect the delicate brain. Of the eight bones, 

 four are paired : the two parietals, which form a large part of the crown of 

 the head, and the temporals, which inclose the ear cavities. Of the four sin- 

 gle bones, two are easily found; the frontal, forming the forehead and upper 

 part of the eye sockets, and the occipital, covering the base of the brain. In 

 the occipital bone is a large opening, through which, in life, the spinal cord 



