XVT.] STRIPED OR STRIATED MUSCLE. 193 



10. Grooving on Smooth Muscular Fibres. Harden the muscular coat of 

 the small intestine of a cat in chromic and bichromate fluid or in Flemming's 

 fluid. Stain and cut sections in paraffin. (H) Observe the polygonal areas, 

 but note that fine intercellular bridges connect adjacent cells (fig. 166). 

 The surface of each cell seems to be grooved with canals, but what these canals 

 contain is not known. In each cell the cut ends of fine fibrils are seen. 



LESSON XVI. 

 STRIPED OR STRIATED MUSCLE. 



Striped Muscle sometimes called voluntary or skeletal muscle 

 occurs in the muscles of the skeleton, pharynx, upper half of 

 the oesophagus, diaphragm, the sphincter of the bladder, external 

 anal sphincter, and the muscles of the outer and middle ear. 

 The muscular fibres of the heart are also striped, but they are 

 involuntary. 



A Muscular Fibre is cylindrical in form, and tapers at its 

 extremities. They vary in breadth from 10 to 50 fi. (^Vo" TSTT 

 inch), but they are broadest in the muscles of the extremities. 

 The fibres are i to i^- inches in length. 



A muscular fibre consists of the following parts : 



(i.) Sarcolemma, or sheath. 



(2.) Sarcous substance, which is transversely striated. 



( 3 . ) Muscle-corpuscles. 



1. The Sarcolemma (H). (i.) To avoid the effect of the con- 

 tractility of the muscle, kill a frog several hours before it is 

 required. Dissect out the sartorius muscle, because it is com- 

 posed of parallel fibres. Tear off a thin strip, and with needles 

 tcaso it in iU*ti1lnd water. 



(a.) Observe the cylindrical shape of the fibres, marked trans- 

 versely by alternate light and dim stripes. Run the eye along 

 the edge of a fibre, and perhaps a clear, transparent bulla or bleb 

 will be seen. If so, it is the Sarcolemma raised from the subjacent 

 sarcous substance by water diffusing into the fibre (Hg. 167, A). 



(/A) The surcolenima is a clear, transparent, colourless, homo- 

 geneous clastic membrane, forming a tubular sheath for the sarcous 

 substance. It is allied to, but not identical with, elastic tissue. 

 It is much tougher and less easily ruptured than the sarcous sub- 

 .stancc which it contains. 



(ii.) A much better plan is the following: Tease out a few 

 18 N 



