position,  called  the  ANATOMICAL  POSITION, is  used  as  a  point  of  reference.  This  anatomical position is assumed when the body stands erect, with arms hanging at the sides, and palms of the hands  turned  forward  (fig.  3-2). Other  commonly  used  anatomical  terms  in- clude  the  following: Anterior or ventral—toward the front, or ven- tral  (pertaining  to  the  belly;  abdomen),  side  of  the body. Posterior or dorsal—toward the back, or dor- sal,  side  of  the  body. Medial—near  or  toward  the  midline  of  the body. Lateral—farther  away  from  the  midline  of  the body. Internal—inside. External—outside. Proximal—nearer the point of origin or closer to  the  body. Distal—away from the point of origin or away from  the  body. Figure  3-2 .—Anatomical  position. Superior—higher  than  or  above. Cranial—toward  the  head. Caudal—toward  the  lower  end  of  the  body. Inferior—lower  than  or  below. Erect—normal standing position of the body. Supine—lying  position  of  the  body,  face  up. Prone—lying position of the body, face down. Lateral  recumbent—lying  position  of  the  body on either side. Peripheral—The  outward  part  or  surface  of a structure. CHARACTERISTICS  OF  LIVING MATTER All  living  things,  animals  and  plants,  are ORGANISMS  that  undergo  chemical  processes by which they sustain life and regenerate cells. The difference between them is that animals have sen- sations  and  the  power  of  voluntary  movement  and require oxygen and organic food. Plants require only carbon dioxide and inorganic matter for food and  have  neither  voluntary  movement  nor  special sensory  organs. In man, some of the characteristic functions necessary  for  survival  include  digestion, metabolism,  and  homeostasis.  DIGESTION  in- volves  the  physical  and  chemical  breakdown  of the  food  we  eat  into  its  simplest  forms. METABOLISM  is  the  process  of  absorption, storage, and use of these foods for body growth, maintenance, and repair. FIOMEOSTASIS is the body’s  self-regulated  control  of  its  internal  en- vironment. It allows the organism to maintain a state of constancy or equilibrium, in spite of vast changes in the external environment. THE CELL The smallest unit of life, the cell, is the basic structural unit of all living things and a functional unit  all  by  itself.  It  is  composed  of  a  viscid, jellylike  substance,  called  PROTOPLASM,  upon which depend all the vital functions of nutrition, secretion,  growth,  circulation,  reproduction,  ex- citability,  and  movement.  As  such,  protoplasm has  been  called  “the  secret  of  life.” A typical cell is made up of the plasma mem- brane,  a  nucleus,  and  the  cytoplasm. The  PLASMA  MEMBRANE  is  a  selectively permeable  membrane  surrounding  the  cell.  In addition  to  holding  the  cell  together,  the  mem- brane  selectively  controls  the  exchange  of 3-2