ELECTRO-PHYSIOLOGY 



CHAP. 



distinction between oblique striation and cross-striation proper, 

 so that one and the same cell may present oblique or transverse 

 striae under different conditions. It seems more probable that 

 the effect is due partly to different states of contraction 

 in adjacent fibrils, partly to a longitudinal displacement 

 (transposition) of the fibrils. 



In Vertebrates also, in the adult state, it is exceptional to 

 find transversely striated uni- or binuclear muscle-cells ; they 

 occur in cardiac muscle, and in a peculiar development of 

 the endocardium of ruminants, horses, pigs, and other mammals, 

 and in certain birds. As a rule, the elements of cardiac muscle 



either resemble the 

 smooth, spindle- 

 shaped fibre-cells 

 (fishes, amphibia), 

 though they ex- 

 hibit many irregu- 

 larities of processes 

 and branches, or 

 form somewhat ir- 

 regular cylindrical 

 or flattened cell- 

 bodies, anastomos- 

 ing at the ends 

 with the adjacent 

 elements in a net- 

 work of branches 

 by means of short broad processes, of which the smooth superficies 

 are closely applied together (mammals, birds, reptiles) (Fig. 15). 

 In many cases the component cells are still clearly visible ; in 

 others they have disappeared, or become hard to recognise. 



These principal types of cardiac muscle are connected by many 

 transitional forms. As so often in the elements of smooth 

 muscle, the cardiac muscle-cells form inter se a physiological as 

 well as an anatomical continuum, being, like many epithelia and 

 endothelia, united by a cement substance, which stains black 

 with AgN0 3 , and through which transmission of the excitatory 

 process is apparently effected. Whether there is here the 

 same anastomosis of adjacent cell-bodies by bridges of protoplasm 

 as in many smooth muscles, has not been determined. 



FIG. 15. Isolated cells of cardiac muscle. A, from Man ; B, from 

 Rana temporaria. (Schiefferdecker.) 



