FORMS OF MUSCLE. 



121 



FIG. 50. Diagrams il- 



.single tendon at each end as , Fig. 50; 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 running right 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 

 attached obliquely to it: such muscles (b, ABC 

 Fig. 50) are called penniform or feath- 

 er-like; or a tendon runs obliquely down 

 the middle of the muscle and has the 

 iibres of the belly fixed obliquely on 

 each side of it (c, Fig. 50), forming a 

 bipenniform muscle: or even two ten- 

 dons 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 as well as at each end of it; such 

 muscles are called digastric. A muscle 



Of this form (Fig. 51) is found in COn- mu^le;c,abipenmforin 



nection with the lower jaw. It arises 

 by a tendon attached to the base of the skull; from there 

 its first belly runs downwards 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 chin, where it ends in a tendon 

 inserted into the lower jaw. Running along 

 the front of the belly from the pelvis to the 

 chest is a long muscle on each side of the 

 middle line called the rectus obdonnnis : it 

 is poly gastric, consisting of four bellies sep- 

 arated by short tendons. Many muscles moreover are 

 not rounded but form wide flat masses, as for example 

 the muscle Ss seen on the ventral side of the shoulder-blade 

 in Fig. 48. 



Gross Structure of a Muscle. However the form of 

 the skeletal muscles and the arrangement of their tendons 

 may vary, the essential structure of all is the same. Each 



FIG. 51. A di- 

 gastric muscle. 



