THE HEART 35 



sarcolemma. The nuclei lie at regular intervals inside the fibre ; 

 they are elliptical in shape, 7-16 ft long, 5-9 /* broad, and possess 

 a well-marked chromatin network and a nucleolus. At both poles 

 of the nucleus is situated a mass of granular protoplasm, the 

 sarcoplasm. This sarcoplasm is more richly developed than 

 in voluntary muscle, and contains strongly refractile basophile 

 granules which in the adult are frequently yellow or yellow brown. 

 Their presence, so far as is known, denotes nothing abnormal. 



Running out from the central sarcoplasm between the bundles 

 of fibrils to the periphery of the fibre there is a very delicate proto- 

 plasmic membrane, the sarcolemma, often richly impregnated with 

 fine granules. It is perhaps not so well developed as in striated 

 muscle, and differs in not being of a chitinous nature. 



The contractile substance of the heart muscle fibre is made up 

 of a number of bundles of fibrils, the sarcostyles. These are some- 

 what prismatic in shape, and lie at the periphery of the fibre ; the 

 centre being occupied by the nucleus and the sarcoplasm (Kolliker). 

 The sarcostyles exhibit longitudinal and frequently transverse 

 striation ; the former being due to its composition of fibrils ; the 

 latter to the presence of singly and doubly refractile substances 

 within the fibril. When the sarcolemma running between the 

 fibrils is well marked, the transverse striation is masked. 



There is an intimate fusion between neighbouring fibres a 

 number of fibrils from one fibre becoming detached and passing 

 uninterruptedly into its neighbour. From this it will be seen 

 that only the small amount of protoplasm situated around the 

 various nuclei can be looked upon as being discontinuous and in 

 any way comparable to the original cells (the myoblasts) from 

 which the heart is developed. These cells appear to have be- 

 come fused together to form a syncytium, and in this a common 

 network of fibrils has been laid down. 



The question then arises that, if the lines formerly described 

 by von Eberth as separating the cells of cardiac muscle from 

 each other, do nothing of the kind, what is their function ? Von 

 Eberth thought they were a cement substance binding the cells 

 together, and called them " cement lines " in consequence. This 

 view has been given up. The lines do not separate cells since the 

 fibrils pass through them (v. Przewosky, v. Ebner, M. Heidenhain). 

 In many places, too, it can be seen, particularly in a fresh prepara- 

 tion, that the so-called line does not always go completely across 



