The bone of the upper arm is joined at the shoulder to a large flat bone-the shoulder-blade, which lies behindthe ribs. The shoulder-blade is kept in position in a wonderful way by the collar-bone. This bone stretches from the top of the breast-bone to the shoulder joint, its outer end being firmly fixed to the shoulder-blade. It is this bone which forms the prominentpart of the shoulder. It acts as a rigid bar to brace the shoulder-blade up. The two collar-bones in front and the two shoulder-blades behind form what is known as the shoulder-girdle.
The thigh-bone is joined to the great haunch or hipbone.
Lesson 07
The Oak Stem
"I had often wondered, sir, at the beautiful markings of the various ornamental woods used by the cabinet-maker," said Fred, as they were putting the things away after the lesson. "I think I understand it clearly now.""I want you to be quite clear as to those medullary rays," said Mr. Wilson. "In all these stems there are twokinds of matter. There is the hard, fibrous, woody tissue and the softer tissue of the pith. In the young tree you have seen that the stem is almost all pith, and that the pith is the channel for the upward passage of the sap.
