340 



THE ANIMALS AND MAN 



There are certain other muscles that form expanded 

 membranes for enclosing cavities. These have no definite 



point of insertion. Such 

 a sheet of muscle by its 

 contractions and relaxa- 

 tions exerts a pressure 

 that affects the move- 

 ments of the contents 

 of the cavity. Examples 

 of this we have already 

 found in the case of the 

 muscles of the heart and 

 arteries. Such also are 

 the muscles of the 

 oesophagus, stomach and 

 intestines. Muscles of 

 this type have been called 

 involuntary muscles be- 

 cause they are regula- 

 ted by the nervous sys- 

 tem without any control 

 of the will. Under the 

 microscope these mus- 

 cles present no appear- 

 ance of striations and so 

 Fig. 174. Deep view of muscles and ten- have been called non-Stri- 



dons of right shoulder. A, brachialis dfgj, muscles. 



anticus; B, tendon of insertion of bi- t»i j j - 



ceps (biceps removed); C.coracoid pro- Blood and nervC SUp- 



cess of scapula; CI, clavicle; H, ply. — Since every muscle 



humerus; Sc, scapula with attached of the body muSt be Well 

 subscapularis muscle. T-T, triceps. ,. , .. , . , 



(After Allen Thomson.) supplied With nutriment 



and oxygen for its meta- 

 bolism and for the work it performs, all muscles of the 

 body are richly supplied with blood capillaries. These pene- 

 trate the connective tissues that separate the muscle fibers. 



