25 



LESSON IV. 

 THE SKELETON (continued). 



THE BONES OF THE LIMBS. 



EACH of the upper extremities consists of the shoulder, the upper 

 arm, the forearm, the wrist, and the hand. The bones of these 

 limbs may be classified as follows : 



Clavicle or collar-bone } ^ ., c ., 7 , , . 



Scapula or shoulder-blade j T g e *er forming the shoulder-girdle. 



Humerus or bone of the upper arm. 



Ulna ) T iU , 

 Radius 1 ^^ farearm. 



Carpal or wrist-bones. 



Metacarpal bones, in the /#/;;/ of the hand. 



Phalanges at finger-bones. 



The clavicle (Lat. davis, a key) is so called from its fancied 

 resemblance to an ancient key. It is commonly known as the 

 collar-bone. One end of it articulates with the top of the sternum, 

 and the other extremity forms a joint with the scapula near its 

 junction with the bone of the upper arm. The clavicle tends to 

 keep the shoulders back. It is short and imperfectly formed in 

 the rounded shoulders of the cat and the dog ; and in the horse 

 and the sheep it is wanting. It forms, however, an essential part 

 of the skeleton of the monkey, the squirrel, and other climbing 

 animals. 



The scapula or shoulder-blade is triangular in form ; it con- 

 sists of a broad flat portion, and a prominent ridge or spine at the 

 back of this. The front surface is smooth and concave, and glides 

 over the back convex surface of the chest. The outer end of the 

 clavicle articulates with one of the two processes which project 

 from the top of the scapula, and is attached to the other process 

 by means of strong ligaments. At the upper and inner part of the 

 scapula there is a shallow concave surface the glenoid cavity 

 (Gr. glene, the pupil ; and eidos, form) which receives the rounded 

 head of the bone of the upper arm. It will thus be seen that the 

 scapula is united to other bones only at or near the shoulder-joint. 

 It has, therefore, great freedom of motion. 



The humerus or bone of the upper arm is very strong. It 

 consists of a long portion called the shaft, and two enlarged ex- 

 tremities called the heads. As already mentioned, the upper head 



