THE SKIN AND SKELETON. 
U7 
shin-bone; and the fibula, or splint-bone. The rounded 
head of the femur fits into a cavity ( acetabulum ) in the 
pelvic arch, while the lower end articulates with the tibia, 
and sometimes (as in Birds) with the fibula also. An ex¬ 
tra bone, the j patella, or knee-pan, is hung in a tendon in 
front of the joint between the femur and tibia of the high¬ 
er animals. The foot is made up of the tarsus , or ankle; 
the metatarsus , or lower instep; and the phalanges, or 
toes. The toes number from 1 in the Horse to 5 in Man. 
Certain parts of the skeleton, as of the skull, are firmly 
joined together by zigzag edges or by overlapping; in 
either case the joint is called a suture. But the great 
majority of the bones are intended to move one upon an¬ 
other. The vertebrae are locked together by their proc¬ 
esses, and also by a tough fibrous substance between the 
centra, so that a slight motion only is allowed. The limbs 
furnish the best examples of movable articulations, as the 
ball-and-socket joint at the shoulder, and the hinge-joint 
at the elbow. The bones are held together by ligaments, 
and, to prevent friction, the extremities are covered with 
cartilage, which is constantly lubricated with an unctuous 
fluid called synovia. 
CHEMICAL COMPOSITION OF BONES. 
Cod. 
Tortoise. 
Hawk. 
Man. 
Phosphate of Lime, with trace of 
Fluoride of Lime. 
57.29 
52.66 
64.39 
59.63 
Carbonate of Lime. 
4.90 
12.53 
7.03 
7.33 
Phosphate of Magnesia. 
Sulphate, Carbonate, and Chlorate 
2.40 
0.82 
0.94 
1.32 
of Soda. 
1.10 
0.90 
0.92 
0.69 
Glutin and Chondrin. 
32.31 
31.75 
25.73 
29.70 
Oil. 
2.00 
1.34 
0.99 
1.33 
100.00 
100.00 
100.00 
100.00 
