HISTOGENESIS AND STRUCTURE 



95 



fibers and are surrounded by an oval aiva of undifferentiated granular 

 >a ivoplasm. The cardiac libers and their brandies contain peripheral 

 nivofibrils, which during growth of the muscle arise by longitudinal 

 splitting of the original fibrils and take position progressively toward the 

 center. Cardiac- muscle thus consists of a slender axial core of undilTer- 

 eiitiated sarcoplasm swelling to an oval, more expansive mass where the 



FIG. 102. A GROUP OF MYO- 



BLASTS PROM THE HEART 

 MUSCLE SYNCYTIUM OF A 

 48 HOUR. CHICK EMBRYO. 



Showing myofibrils, myo- 

 chondria and mitochondria. 

 The latter are the deeper 

 staining granules. Meves' 

 technic. X 2000. 



FIG. 103. CARDIAC 

 MUSCLE OF GUINEA 

 PIG, SHOWING SEV- 

 ERAL BRANCHES, 

 CROSS STRIATIONS 

 (GROUND M E M - 



BRANES) AND A Xuil- 



BER OF INTERCALATED 

 DISKS. 



Zimmerrnann's tech- 

 nic-. X 1000. 



nuclei arc located ; this core is surrounded by successive rows of myofibrils 

 arranged in groups representing Cohnheim's fields in transverse section; 

 and the whole is invested by a delicate sarcolemma. The striations of 

 the fiber result from the fact of a transverse alignment of identical areas 

 in adjacent fibrillw a correspondence which indicates a definite func- 

 tional stimulus to a structural modification ( Fig. !(>.">). The sarcoplasni 

 contains mitochondria (Fig. 1<"'^), lipoid, albuminoid (interstitial gran- 



