106 



MUSCULAR TISSUE 



FIG. 117. STRIATED 

 MUSCLE FIBERS RUP- 

 TURED BY TEASING, 

 SHOWING THE SARCO- 



LEMMA. 



a, ruptured end of the 

 muscle fiber; B, a bundle 

 of fibrils projecting from 

 the torn end; m, a muscle 

 fiber; n', a nucleus of the 

 muscle cell; at p, the 

 muscle substance has 

 shrunken away from the 

 sarcolemma; s, sarcolem- 

 ma. Moderately magni- 

 fied. (After Ranvier.) 



oped in a small amount of granular sarcoplasm. 

 The sarcolemma is a homogeneous, plastic, non- 

 nucleated membrane, the representative and 

 product of the cell membrane of the original 

 myoblasts. 



In routine laboratory preparations only the 

 Z, Q, and J stripes are conspicuous. Meigs 

 (Zeitschr. allg. Phys., 8, 1, 1908) recognizes at 

 most only three different substances in striped 

 muscle sarcostyles (fresh wing muscle of fly) : 

 Q, Z, and M. He regards J and H as optical 

 effects dependent upon the reflection of light by 

 the Z and M membranes. 



Thulin (Arch. mikr. Anat, 86, 3, 1915) 

 records the absence of both Z and M membranes 

 in the wing muscles of certain insects (Coleop- 

 tera) and the analogous (pectoral) muscles of 

 birds and bats. 



' The perinuclear sarcoplasm contains filar and 

 granular mitochondria. Both the perinuclear 

 and interfibrillar sarcoplasm contain also fat 

 granules and globules (liposomes), interstitial 

 granules of Kolliker and glycogeu. 



Heidenhain (Anat. Anz., 44, 11-12, 1913) has 

 conclusively shown that in the trout embryo the 

 progenitor (the manner of whose origin is un- 

 known) of the definitive myofibrillae is a single, 

 stout, deeply staining column, close to the nuclear 

 wall externally, which undergoes a succession of 

 radial and concentric longitudinal divisions. This 

 observation would seem to dispose of the assump- 

 tion of a direct mitochondrial origin of myofibril- 

 lae in this form at least, in the manner of the 

 current descriptions. And this conclusion is 

 strengthened by the demonstration of mitochon- 

 dria throughout the earlier development (Fig. 

 116). 



Skeletal muscles develop from a portion of 

 the mesodermic segments qr primitive somites, 

 called the myotomes. The myoblasts pass through 



