516 Caroline McGill. 



The coarse myofibrillse, especially those lying close to the periphery 

 of the muscle cell, have to be differentiated from the elastic fibers 

 which, in some muscle, lie in the connective tissue immediately sur- 

 rounding the muscle protoplasm, or even embedded in the peripheral 

 protoplasm itself (Fig. 25, McGill (1), 1907). This is especially 

 true in material stained with iron htematoxylin. With this stain 

 both coarse myofibrillse and elastic libers are intensely black. In 

 longitudinal section is it usually comparatively easy to tell them 

 apart, for the elastic fibers are more wavy than the coarse myofibrillse. 

 Moreover, the elastic fibers are always around the periphery, while 

 the coarse myofibrillse may be scattered throughout the cell proto- 

 plasm. With Weigert'si elastic tissue stains the elastic fibers can be 

 differentiated from the myofibrillse. 



3. Is^'uclei. 



The nucleus of resting smooth muscle is a much elongated, rod- 

 shaped structure many times as long as wide. In the material 

 studied the nuclei vary in length from twenty micra in chicken 

 intestine to eighty micra in Necturus intestine. Schultz, in a large 

 number of forms studied, found the shortest nuclei in smooth muscle 

 of the dove, thirteen micra, and the longest in the intestine of Pro- 

 teus, seventy-two micra. The j)roportion of length to width varies 

 extremely. In muscle of a primitive type, as in the syncytia shown 

 in Figs. 7 and 14, the nuclei are very wide in proportion to their 

 length. In arterial muscle the nuclei are extremely long and narrow. 

 Figs. 5, 82. 



In muscle of the marked syncytial type the nuclei are usually 

 located at the nodal points, the long axis parallel with the long axis 

 of the bundles of myofibrilltTe. In apparently isolated fibers, as in the 

 nmscle of the carotid of the ox, the nuclei usually lie close to the 

 center of the fiber. Occasionally an eccentric position is observed. 

 The nucleus may lie so close to one side of the fiber that one surface 

 appears free from the cytoplasm. Figs. 19, 25. An eccentric posi- 

 tion of the nucleus Avas frequently observed in intestinal muscle of 

 ISTecturus, chicken, and dog. This position of nucleus was described 

 by Kolliker in amphibian muscle and l)y Lenhossek in cat muscle. In 

 the chicken the nuclei are often nearer one pole of the fiber than the 



