COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 49 



The small amounts of magnesium, sodium, potassium, carbon 

 dioxid and chlorin appear to be as essential ingredients of bone 

 ash as its calcium or phosphorus. 



82. Cartilage, ligament, tendon, elastic tissue. Not all 

 of the cartilaginous ground work of the skeleton as laid 

 down in the embryo is converted into bone. In particular, the 

 end surfaces of bones at a joint consist of cartilage, which in 

 other cases forms a connecting link between adjoining bones, 

 as, for example, the cartilage connecting the ribs with the 

 breast bone, thus allowing a limited degree of motion. At the 

 joints proper, the bones are held in place, and the direction and 

 extent of their motions limited, by the ligaments, while the 

 muscles which serve to impart motion to the various parts of 

 the body are attached to the bones by means of tendons. In 

 many cases the intercellular substance of the supporting tissue 

 contains fibers of elastin. When these fibers are abundant the 

 tissue is elastic in contrast to the ligaments and tendons of the 

 joints, which are almost inextensible. A striking instance is 

 afforded by the elastic band (Ligamentum mtchce) which runs 

 along the back of the neck of quadrupeds and supports the 

 weight of the head. Another example is furnished by the layer 

 of elastic tissue contained in the walls of the arteries which 

 gives them a certain degree of resilience to the pressure of the 

 blood pumped by the heart. 



The " organic " portion of all these forms of supporting tis- 

 sue, like the organic portion of the bones, consists essentially of 

 different proteins belonging to the group of albuminoids. 



83. Connective tissue. This name is sometimes applied 

 to all the various forms of supporting tissue, since they also 

 serve to connect the various organs of the body. In a more 

 ordinary and limited sense, however, it is used to designate a 

 form of supporting tissue of which the most familiar example 

 is the tissue lying between the skin and the underlying muscles, 

 or lean meat, and serving to connect them together. A more 

 careful examination shows that this subcutaneous connective 

 tissue is continuous with other similar tissue which extends 

 between the single muscles and serves at the same time to de- 

 limit them and connect them. Not only so, but this sheath 

 of connective tissue extends into the muscle itself, dividing it 

 into muscular bundles or fasciculi and these again into secondary 



