STEUCTUKE OF THE HUMAN MECHANISM 7 



The human mechanism is composed of different parts, such 

 as head, neck, trunk, arms, hands, legs, and feet, and each of 

 these in its turn is composed of lesser parts. Arms and hands, 

 for example, are covered by skin, which may be moved over 

 underlying soft parts ; at the ends of the fingers the place of 

 the skin is taken by nails, while scattered over and emerging 

 from its surface are hairs. Through the skin may be seen the 

 veins, which may be emptied of the purplish blood they con- 

 tain by pressing one finger on a part of the vein near the 

 finger and pushing another finger along the vein toward the 

 wrist ; so long as pressure is maintained by both fingers 

 the vein remains collapsed, but on removing the first finger 

 it fills again with blood. Finally, through the soft parts 

 (flesh) may be felt the hard bones. In general these various 

 parts of which the body is composed are known as its organs, 

 and because it possesses organs it is called an organism (p. 3). 



1. The skin. The body is everywhere covered by a com- 

 plex protective and sensitive organ, the skin. Only the eyes 

 and nails seem to be exceptions ; but as a matter of fact the 

 exposed surface of the eye is covered by a very thin, trans- 

 parent portion of the skin, and the nails are really modified 

 portions of skin. 



2. Subcutaneous connective tissue. On cutting through the 

 skin we find that it is bound to the underlying flesh (chiefly 

 meat or muscle) by what is known as connective tissue, the 

 structure of which we shall study in the next chapter. Mean- 

 while we may notice that it contains blood vessels, that at 

 some places it is more easily stretched than at others, and 

 that when a flap of skin is pulled away from the muscles, 

 this subcutaneous tissue fills with air. It often contains large 

 quantities of fat. 



Such practice may well precede drawing from an actual dissection and 

 will pave the way to the latter. At all events let the student understand 

 thoroughly that in the present chapter the figures, supplemented if possible 

 by actual dissections, form the main objects of study ; the text is strictly 

 subordinate to the figures. 



