MUSCLES. 175 



inch thick and -%^-Q inch in length. Its nucleus is rod- 

 shaped and placed about the centre of the cell, which is 

 delicately striated longitudinally, and which striations 

 are the fibrillae. The involuntary muscle is not con- 

 trolled by the will ; it is found in the walls of the hollow 

 viscera, in many ducts and vessels. The muscle of the 

 heart consists of voluntary or striped muscular fibres which 

 branch and interlace. They have but little investing 

 connective tissue, so little that the existence of even the 

 sarcolemma has been denied. In addition, each fibre has 

 a distinct nucleus. The heart-muscle may be regarded 

 as a blending of the voluntary with the involuntary 

 muscular fibre. 



There are about two hundred and fifty pairs of 

 muscles arranged symmetrically and six or seven single 

 muscles in the human body. They are named according 

 to location, as the subclavius and peroneal; or, according 

 to direction, as the recti ; or, according to shape, as the 

 trapezius ; or, according to attachments, as the sterno- 

 mastoid ; or, according to function, as the abductors and 

 flexors. 



The origin of a muscle is the fixed point from which 

 it acts, and in the extremities is generally the point of 

 attachment nearest the trunk. Muscles are inserted 

 directly without the intervention of tendons, as in the 

 case of facial muscles ; or by tendons and aponeuroses. 

 Tendons are cords of white, fibrous tissue; generally 

 small at their point of attachment ; often rounded ; 

 sometimes flattened. Aponeuroses are thin planes of 

 white, fibrous tissue, by which certain muscles are 

 attached. 



The fasciae are laminae of white, fibrous tissue; differ- 

 ently arranged in different parts of the body. The 

 superficial fascia immediately beneath the skin consists 



