122 ^ MUSCLE TISSUE 



The Muscle Stimuli. In the living body all muscle 

 tissue contracts in response to nerve impulses sent 

 from the central nerve system to the muscles. Experi- 

 mentally and artificially muscles are stimulated to 

 contract by various stimuli, e. g., mechanic pinching, 

 striking, or cutting a muscle; chemic, numerous chemi- 

 cal solutions; thermic, heated object, as hot needle or 

 wire will cause a rapid contraction; electric, as batteries 

 are used by physicians as therapeutic agents or upon 

 animal tissue during experiments in the laboratory. 



Attachments of Muscles. Muscles are attached to 

 bones, cartilages, ligaments, or skin by means of short, 

 or long, rounded fibrous cords called tendons, or by 

 short, flat, fibrous membranes called aponeuroses. All 

 muscles, though they appear to be attached to bone or 

 cartilage, in reality fuse with the periosteum or peri- 

 chondrium at the point of attachment and do not 

 touch the bone or cartilage. Muscles attached to the 

 skin are flat and thin and their fibers fuse with the 

 areolar tissue just beneath the skin, as the muscles of 

 the face. 



Muscles vary as to their form. Some are long, and 

 flat or round; others short, and flat or round; still others 

 triangular and quadrilateral in shape. 



The origin of a muscle is called its head, and the 

 portion which intervenes between the head and 

 the tendon or aponeurosis is termed the belly or body 

 (venter) . 



Muscles derive their names from the part of the body 

 in which they are situated; the tibialis anticus the 

 anterior tibial region, ulnaris ulnar region, radiali?, 

 radial region, etc. ; from the direction their fibers take 

 rectus abdominis, obliquus hallucis, transversalis; 

 according to their use or action flexors, extensors, 

 abductors, adductors, levators, compressors; from 

 their shape deltoid, trapezius, digastric; according 

 to their number of divisions biceps, triceps; from 



