STRUCTURE OF MAN. 21 



the general shape and constitute the features of the counte- 

 nance. 



The head is placed on the top of the back-bone or ver- 

 tebral column, and is capable of a number of motions upon 

 it. The back-bone is the main support of the trunk of the 

 body, and is composed of twenty-four distinct vertebrae, placed 

 one above another, so as to form a kind of pillar or column. 

 The body of each vertebra consists of a solid cylindrical 

 piece of bone, and this is united firmly to those contiguous 

 to it, above and below, by strong and elastic cartilages. The 

 body of the vertebra is solid ; but behind it, and on each 

 side, are projections of bone, called processes, which are 

 arched over and connected together in such a manner as 

 to form a canal from one end of the spine to the other. This 

 canal contains the spinal nerve or marrow, and between the 

 vertebrae are holes, through which branches are sent out to 

 the different parts of the body. 



Seven of the vertebras belong to the neck, twelve to the 

 back, and five to the loins. They are called respectively the 

 cervical, dorsal, and lumbar vertebrae. They increase in 

 size from above, downwards, so that the lumbar vertebrae are 

 much larger, thicker, and stronger than those of the back and 

 neck. To the dorsal vertebrae are affixed twelve ribs on 

 each side, which arch over forwards, and are joined to the 

 sternum or breast-bone by means of cartilage or gristle. In 

 this way they form the cavity of the thorax or chest, which 

 contains the heart and lungs. This cavity is terminated below 

 by a muscular membrane, called the diaphragm or midriff, 

 which extends from the edges of the lower ribs, and stretches 

 across to the back-bone, so as to form a complete curtain or 

 division between the chest and the abdomen which lies be- 

 low it. This is another important cavity, usually called the 

 belly, containing the stomach, liver, spleen, caul, alimentary 

 or intestinal canal, kidneys, &,c. It is formed below by four 

 bones attached to the lower end of the back, which spread 

 out and constitute a sort of basin, called the pelvis. This 

 serves as a solid basis to support all the heavy organs con- 

 tained in the abdomen, which is protected before and at its 

 sides only by skin, fat, and muscles, and has no bones, ex- 

 cept below and behind. 



The limbs of man and other animals are called their ex 

 tremities. The arm, or upper extremity, is composed of the 

 shoulder, which has two bones, the collar-bone and shoulder- 

 blade, by which it is connected with the trunk ; the arm, 



