Xlll] STRIATED MUSCLE 101 



at a certain stage of the decoloration of the fibres this is very 

 distinct. 



4. Cut through the skin ui the mid ventral line in 

 a small frog, lift up the flap of skin on one side over 

 the middle of the sternum, a thin band of muscle, the 

 sterno-cutaneous muscle (m. cutaneus pectoris), will be 

 seen running from the skin downwards towards the 

 lower part of the sternum. Cut through the skin 

 above and below the muscle, and keeping it well 

 stretched, pour a little '5 p.c. osmic acid over it. In a 

 minute or so the muscle will be fixed (the connective 

 tissue surrounding the muscle may be torn away with 

 fine forceps but in doing this there is considerable danger 

 of injuring the muscle and its nerve) ; cut it out, being 

 careful to cut the upper end as close as possible to the 

 skin ; place it in osmic acid for 15 to 30 minutes, wash 

 with water. Divide the muscle transversely near its 

 upper end. Mount in glycerine, the upper end having 

 the outer surface, and the lower end the inner surface 

 uppermost (the latter will be required in Less. xiv. 



10). 



Observe at the upper end of the muscle the endings 

 of the muscular fibres ; these will probably be covered 

 by a good deal of connective tissue, but the rounded or 

 conical ends of the muscle-substance of the fibres and 

 the continuation of the sarcolemma into the connective 

 tissue (tendon) will be seen. 



The muscle, after it has been treated with osmic acid and 

 washed, may be stained with picrocarmine ; or the muscle of the 

 opposite side may be fixed with alcohol (Less. x. 9) and 

 stained with picrocarmine ; thus the nuclei will be brought out. 

 The nerve fibres stain better if the muscle after osmic acid is 

 placed for a day in 30 p.c. alcohol. 



