136 



THE TISSUES. 



has been described as intercellular bridges may readily be seen in 

 corrosive sublimate preparation, stained in Mallory's differential 

 connective-tissue stain, especially in portions of the preparation not 

 well fixed. In such preparation the so-called intercellular bridges 

 end at the connective membranes separating cells, to which they 

 are attached but which they do not penetrate. Nonstriated muscle- 

 cells develop from the mesenchyme. (Exceptions to this statement 

 appear to be found in the nonstriated muscular tissue of the iris 

 [Szili] and in the sweat-glands, where the muscular tissue appears 

 to be developed from ectodermal cells.) The nuclei of the mesen- 

 chymal cells elongate and become rod-shaped, with oval ends, while 

 the cells become spindle-shaped, the protoplasm staining somewhat 

 more deeply than that of the surrounding mesenchymal cells. 

 Further details as to the development of nonstriated muscular tissue 

 are lacking. 



2. STRIPED MUSCLE-FIBERS. 



Soon after the segmentation of the mesoderm begins, certain 

 cells of the mesoblastic somites or myotomes commence the forma- 

 tion of muscle-substance in their interior, a process which is accom- 

 panied by increase in the number of nuclei, the formation of a mem- 

 brane, a lengthening of the cells, and the appearance of fibrils in 

 the peripheral protoplasm of the cells. 



^K Free ending. 



Nucleus. 



Fig- 93- Cross-section of striated muscle-fibers : 

 I, Of man ; 2, of the frog. The relations of the 

 nuclei to the muscle-substance and sarcolemma are 

 clearly visible ; X 670. 



Fig. 94. Muscle-fiber from 

 one of the ocular muscles of a 

 rabbit, showing its free end ; 



X.I75- 



Voluntary or striated muscle-cells are large, highly differen- 

 tiated, polynuclear cells, which may attain a length of 12 cm., with 

 a width of 10 100 fj.. They are consequently known as muscle-fibers. 

 Their free ends are usually pointed ; the ends attached to tendon 

 rounded (Fig. 94). 



