SPINE OF THE VERTEBRATA. 



generally twelve in number on each side, though jn 

 some instances they are found to be thirteen, and more 

 rarely only eleven. They are distinguished into true 

 and false ribs. The seven upper ones, which are artic- 

 ulated, or joined to the sternum, c, are called true ribs, 

 while the five lower ones, which are not immediately 

 attached to the sternum, or breast-bone, but to a cartilage 

 connected with it, are called the false ribs. The other 

 extremities of the ribs are articulated by small heads to 

 the vertebrae, and secured by a ligament, so as to allow of 

 a small motion upward and downward, but in no other 

 direction. 



236. The use of the ribs is to give form to the thorax, 

 to cover and defend the lungs and heart, which are situ- 

 ated within them ; and also to assist in breathing, by their 

 alternate elevation and depression. 



237. The sternum, c, or breast-bone, it is well known, 

 h situated in front of the thorax. In young people, this 

 bine is hi several parts, united by cartilages ; but as we 

 advance in life these cartilages ossify, or are changed 

 into bone. Its shape is oblong, and its external surface 

 convex. To its edges are immediately articulated the 

 seven upper ribs. 



238. The clavicle, b, has its name from the Latin clavis, 

 which appears to come from clando, to shut, this bone 

 resembling in shape an ancient key. It is usually called 

 the collar bone, and is placed at the upper part of the 

 breast, or root of the neck, extending across from the 

 tip of the shoulder to the upper part of the sternum. It 

 is a round bone, curved, somewhat into the shape of 

 the italic S. It supports, and maintains the shoulder in 

 its proper place, and prevents it from falling forward 

 toward the breast. Its outer end is firmly fixed to the 

 upper part of the scapula, or shoulder-blade. Animals 

 which employ their fore feet as hands are furnished with 

 this bone, as the monkey-tribe and squirrels ; while those 



What is the number of ribs in the human skeleton? How are they 

 listinguished ? To what part are the seven upper ribs articulated in 

 front ? How are the anterior ends of the five lower ribs secured? How 

 are the posterior ends of all the ribs secured ? What are the uses of the 

 ribs? What is said of the sternum? Whence is the name clavicle? 

 What is the common name of this bone ? To what parts is the clavicle 

 articulated? What animals beside man have this bone? 



