HISTOGENESIS AND STEUCTURE 



95 



fibers and are surrounded by an oval area of undifferentiated granular 

 sarcoplasm. The cardiac fibers and their branches contain peripheral 

 myofibrils, 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 undiffer- 

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



FIG. 102. A GROUP OF MYO- 

 BLASTS FROM THE HEART 

 MUSCLE SYNCYTIUM OF A 

 48 HOUR. CHICK EMBRYO. 

 Showing myofibrils, myo- 



chondria and mitochondria. 



The latter are the deeper 



staining granules. M eves' 



technic. X 2000. 



FIG. 103. CARDIAC 

 MUSCLE OF GUINEA 

 PIG, SHOWING SEV- 

 ERAL BRANCHES, 

 CROSS STRIATIONS 

 (GROUND MEM- 

 BRANES) AND A NUM- 

 BER OF INTERCALATED 

 DISKS. 



Zimmermann's tech- 

 nic. X 1000. 



nuclei are 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 fibriUae a correspondence which indicates a definite func- 

 tional stimulus to a structural modification (Fig. 103). The sarcoplasm 

 contains mitochondria (Fig. 102), lipoid, albuminoid (interstitial gran- 



