THE STRUCTURE OF VOLUNTARY MUSCLE 205 



The sartorius muscle consists of a thin band of muscle fibres 

 running parallel from one end of the muscle to the other. It lies on 

 the ventral surface of the thigh, arising from the symphysis pubis by 

 a thin flat tendon, and is inserted by a narrow tendon into the inner 

 side of the head of the tibia. On account of the regularity with, which 

 its fibres are disposed, this muscle is of especial value in experiments 

 on the local conditions of a muscle fibre accompanying its activity. 



Cruralis -^________ 



^^^ .Sartorius 



Add. inagn. __ __^ == _^_ 



Add. magn. 



Gracilis 



Tib. ant. long. 



Gastrocnemius 

 Tib. post. 

 Tibia 



Tendo Acliillis 



FIG. 41. Muscles of hinder extremity of frog. (After ECKEE.) 



When a greater mass of approximately parallel fibres is necessary, 

 recourse may be had to a preparation consisting of the gracilis and 

 semi-membranosus muscles together. This latter muscle lies dorsally 

 to the gracilis muscle which is shown in the illustration. 



Other muscles in the frog used for particular purposes are the 

 mylohyoid and the dorsocutaneous muscles. The mylohyoid muscle 

 of the frog, which lies on the ventral surface of the tongue, has the 

 advantage that its fibres lie in close contact with a lymph-space 

 occupying the centre of the tongue. If any drug be injected into 

 this lymph-space it acts with extreme rapidity on the muscle fibres, 

 so that the tongue- preparation of the frog is a useful one for the study 

 of the action of different substances on muscle fibres. 



