2 ANATOMY AND PHYSIOLOGY 



in mind. Thus, the anterior surface of the hand is always the 

 palm; and, if we speak of any part as situated to the right we 

 mean that it is nearer to the right side of the body which we are 

 studying (which for convenience we will call the "subject"), 

 but it has no relation whatever to the right side of the student. 

 Of course the words superior and inferior are easily understood, 

 but the use of the words medial and lateral (formerly internal 

 and external) requires special mention. Imagine a line drawn 

 through the middle of the head and trunk and striking the floor 

 between the feet, thus dividing the body into right and left 

 halves. This is called the median line. Any part or surface of 

 one-half of the body is said to be medial to another part if it is 

 nearer the median line while in the anatomic position, or lateral 

 to another part if it is farther from the median line. 



All-of these terms once applied to a part of the body belong to 

 it always. For example, the little finger is always medial to the 

 others and the great toe is likewise medial, because these relations 

 are established once for all while the subject is in the anatomic 

 position. Likewise, the palm is the anterior surface of the hand 

 even if it be temporarily turned backward. 



The words exterior 'and interior are applied to the parts of the 

 body which are on the surface or within, respectively. 



Proximal means nearer to the head; distal, farther from the 

 head. Thus we may speak of the proximal end of the finger, or 

 the distal end of a toe, or the proximal end and distal end of an 

 arm or a leg. 



Certain words have been so long applied in a special sense in 

 connection with anatomic relations and physiologic processes 

 that usage has made them technical, that is, they have come to 

 possess a professional meaning. 



Hilum (literally a little thing) is applied to a place on the 

 surface of an organ; a depression usually, where the vessels and 

 nerves enter and leave it. Thus, we see the hilum of the kidney, 

 of the lung, of the spleen. The hilum is always found on the 

 medial or most protected surface of an organ. (In the case of the 

 liver it is on the inferior surface and is called the porta or gateway.) 



Sivus (literally a hollow or indentation) is applied in anatomy 

 to a hollow or enlarged space within an organ, containing either air 

 or fluid. Air sinuses are hollow spaces (almost enclosed), con- 



