STBUCTUBE OF THE HUMAN MECHANISM 9 



Fig. 161). In either case the shortening of the muscle brings 

 closer together the bones to which it is attached. 



5. Definition of some anatomical terms. Before proceeding 

 further we must agree upon the exact meaning of certain 

 anatomical terms. We often speak of one part of the body as 

 being "above" or "below," "before" or "behind," another. 

 Such terms, however, are confusing, because their meaning de- 

 pends upon the position of the body at the time they are used. 

 For example, when one is lying on his back the head is in 

 front of, or before, the 

 trunk ; but when he is 

 standing on his feet it 

 is above the trunk. 



Now the body is 

 certainly divided into 

 right and left halves, 

 which are much alike 

 externally, though this 

 likeness is not so 

 marked in the internal 

 parts. Right and left 

 then have their ordi- 

 nary meanings, and 

 that without regard to 



flip vnrinn^ nnditinn<* ^, skin ; 7?, subcutaneous connective tissue, bind- 

 VailC ing the skin to the muscles D and continuous 



with the connective tissue which binds together 

 the muscles ; C, blood vessels and nerves 



FIG. 1. Cross section of arm 



the body may take. 



To indicate that any 

 part is nearer the head than another part, we say that the 

 former is anterior to the latter ; to indicate that the latter is 

 further away from the head, we say it is posterior to the former. 



Finally, the region popularly known as the back is called 

 dorsal (Latin dorsum, " back "), that opposite the back being 

 called ventral (Latin venter, "belly"). Thus the nose is on 

 the ventral side of the head; the toes are at the posterior 

 extremity of the foot. 



