116 



THE HUMAN BODY. 



the origin of the muscle, and the forearm attachment, P, the 

 insertion. It is clear, however, that this distinction in the 

 mobility of the points of fixation of the mnscle is only rela- 

 tive, for, by changing the conditions, the insertion may become 

 the stationary and the origin the moved point; as for instance 

 in going up a rope " hand over hand." In that case the radial 

 end of the muscle is fixed and the shoulder is moved through 

 space by its contraction. 



Different Forms of Muscles. Many muscles of the Body 

 have the simple typical form of a belly tapering to a single 

 tendon at each end as A, Fig. 53; but others divide at one 

 end and are called two-headed or biceps muscles; while some 

 are even three- headed or triceps muscles. On the other hand 

 some muscles have no tendon at all at one end, the belly run- 

 ning quite up to the point of attachment; and some have no 

 tendon at either end. In many muscles a tendon runs along 

 one side and the fibres of the belly are at- 

 tached obliquely to it: such muscles (B, Fig. 

 53) are called penniform or featherlike; 

 or a tendon runs obliquely down the middle 

 of the muscle and has the fibres of the belly 

 fixed obliquely on each side of it (C, Fig. 53), 

 forming a bipenniform muscle : or even two 

 tendons may run down the belly and so form 

 a tripenniform muscle. In a few cases a 

 tendon is found in the middle of the belly 



FIG. 53. Diagrams . 



illustrating typical as well as at each end oi it; such muscles 



muscle with a central -\-iii- * * ^ .c j_i j? 



belly and two termi- are called diastric. A muscle of this form 



(Fig. 54) isfonnd in connection with the 



bipenniform muscle. IQ ^ ^ ^ ^^ by ft tend(m attached 



to the base of the skull; from there its first belly runs down- 



wards and forwards to the neck by the side of the hyoid bone, 



where it ends in a tendon which passes through a loop serving 



as a pulley. This is succeeded by a second 



belly directed upwards towards the ciiin, 



where it ends in a tendon inserted into the 



lower jaw. Running along the front of the 



abdomen from the pelvis to the chest is a lonqr 



muscle on each side of the middle line called 



the rectus abdominis: it is polygastric, con 



sisting of four bellies separated by short tendons. Many 



muscles moreover are not rounded but form wide flat masses, 



