204 



PHYSIOLOGY 



end-plate. The neurilemma of the nerve fibre becomes continuous 

 with the sarcolemma, the medullary sheath ends suddenly, while the 

 axis cylinder ramifies in a mass of undifferentiated protoplasm, con- 

 taining nuclei, and lying in contact with the contractile substance of 

 the muscle immediately under the sarcolemma (Fig. 40). This mass 



of protoplasm is known as the 

 'sole plate.' It is not marked 

 in all animals. Thus in the frog 

 the axis cylinder ends in a series 

 of branches at right angles to one 

 another, distributed over a con- 

 siderable length of the muscle fibre. 

 The sole plate in this case seems 

 to be limited to scattered nuclei 

 lying in close contact with the 

 terminal branches of the nerve 

 fibre. So far as we can tell at 

 present, the ultimate ramifications 

 of the axis cylinder end freely and 

 do not enter into organic connec- 

 tion with the contractile substance 

 itself. 



Most of our knowledge on the 

 subject of muscle has been derived 

 from the study of the gastroc- 

 nemius and sartorius muscles of 

 the frog. The position of these 

 muscles is shown in the accom- 

 panying diagram (Fig. 41). The 

 gastrocnemius, which, with the 

 attached sciatic nerve, is most fre- 

 quently employed as a nerve- 

 muscle preparation, forms a thick belly immediately iinder the skin at 

 the back of the leg, and arises by two tendons from the lower end of 

 the femur and the outer side of the knee-joint. The two tendons 

 converge toWards the centre of the muscle, uniting about its middle, and 

 from them a number of short muscular fibres arise, passing backwards 

 and dorsally to be inserted into a flat aponeurosis covering the lower 

 half of the muscle, which ends in the tendo Achillis. On account of 

 this irregular arrangement of the muscular fibres, the gastrocnemius 

 can only be employed when the contraction of the muscle as a whole is 

 the object of investigation. The effective cross- area of the fibres is 

 much greater than the actual cross-section of the muscle, so that, 

 while the actual shortening of the gastrocnemius is but small, its 

 strength of contraction is considerable. 



FIG. 40. Motor end-organ of a lizard, 



gold preparation. (KtifiNE.) 

 n, nerve fibre dividing as it ap- 

 proaches the end-organ; r, ramifica- 

 tion of axis cylinder upon 6, granu- 

 lar bed or sole of the end -organ ; m, 

 clear substance surrounding the 

 ramifications of the axis cylinder. 



