Huber-DeWitt, Nerve-Endings in Muscles. 203 



the larger spindles — compound spindles — as many as twenty may 

 be found. It is stated (Sherrington) that the muscle fibers des- 

 tined to form intrafusal fibers are of the red variety, rich in 

 protoplasm. In muscle-spindles containing more than one in- 

 trafusal fiber, one, two, three, and perhaps even more muscle 

 fibers enter the proximal end of the spindle, and at once divide 

 into two, three, or even four daughter fibers, of round or oval 

 shape ; these are the intrafusal fibers. They usually have a more 

 or less parallel course in the spindle, although in longitudinal sec- 

 tions, they now and then give the appearance of a loose braid, 

 showing that the intrafusal fibers may now and then be more or 

 less twisted in the spindle. The intrafusal fibers are, so far as 

 our observations allow us to assert, enclosed in a sarcolemma, 

 although this is not always distinctly made out in sections, and 

 Sherrington states that "some of the intrafusal fibers are de- 

 void of sarcolemma." The intrafusal fibers show a more or less 

 distinct longitudinal and cross striation, which may usually be 

 made out through the entire length of the fiber. In the mid- 

 dle third of the spindle, the portion described by Sherrington 

 as the equatorial region, the intrafusal fibers possess, according 

 to this observer, the following structure: " The intrafusal fiber 

 often becomes somewhat smaller in diameter and is nearly al- 

 ways circular in section. Its surface zone soon gets thickly 

 encrusted with or almost completely occupied by a sheet of 

 nuclei. Whether these nuclei are strictly part of the muscle 

 fiber is not clear to me. The nuclei are spherical or slightly 

 oval, are clear, and measure about 6 // in diameter. Cross-sec- 

 tions reveal beneath the nuclear sheet a thin tubular layer 

 which is fibrillated. This tubular layer itself invests a central core 

 (4/z "5// ) of hyaline substance, which runs rod-like along the axis 

 of the intrafusal fiber in this region. The cross-section of the fiber 

 thus often displays a nearly complete zone of four to six nuclei 

 around a hyaline centre." We have quoted thus freely from 

 Sherrington's account, because our own observations are not 

 fully in accord with what he has here described. The sheet of 

 nuclei mentioned by him, is not, we believe, a part of the in- 

 trafusal muscle fiber, as, in instances where it was possible to 



