174 



STUDIES IN PHYSIOLOGY 



In the wrist we counted eight carpal bones, and in 

 the ankle seven tarsal bones. During 

 childhood, however, the heel bone consists 

 of two separate bones ; hence until about 

 the fourteenth year both wrist and ankle 

 have eight separate bones. 



5. STRUCTURE OF BONES l 



In the skeleton of vertebrates there are 

 two different types of bone structure. One 

 type can be studied to good advantage 

 from a soup bone ; the other is well shown 

 in a rib of lamb or beef. Since the latter 

 is the simpler, it will be discussed first. 



Structure of a Rib. After the meat or 

 muscle has been removed from a lamb 

 chop, there remains a slender, curving 

 bone, flattened in form, which is the rib. 

 A piece of vertebra often remains con- 

 nected with the thicker end (compare 

 with Fig. 69). When the rib is carefully 

 separated from the vertebra, the two sur- 

 faces that move on each other are found 

 to be covered with smooth, bluish-white 

 cartilage ; this lessens friction. 



If the point of a penknife be pushed 

 into the side of the rib, a thin membrane 

 of tough connective tissue can be raised 

 from the outside of the bone and pulled 

 off in sheets. This is the per-i-os'te-um 

 (Greek pen' = around -f- oste'on = bone). 

 The periosteum is of great importance in 

 connection with the growth of bone, since 

 most of the new bone is formed just be- 

 neath this layer of connective tissue, and 

 by its agency. 

 "Laboratory Exercises," No. 30. 



FIG. 73. Long 

 Bone (Femur). 



A = rounded head 

 which fits into sock- 

 et of hip bone. 



G'= shaft of bone. 



D, E= rough pro- 

 cesses to which mus- 

 cles are attached.- 



F = smooth sur- 

 face of head which 

 articulates with the 

 tibia. 



