94 HISTOLOdY. 



The function of these different parts of the cell is not quite 

 clear. The sarcoplasm dissolves in water, dilute acids, and 

 alkalies, and allows the primitive fibrils to be separated. Sar- 

 coplasm plays some role in the nourishment, increase, and 

 growth of the muscle fibres. It is present in large quantitk-s 

 around the motor nerve-endings, and serves probably to trans- 

 mit the nervous impulse equally through .the cell. 



Cross-striated muscle fibres are found in all the skeletal 

 muscles, the outer muscles of the eye, muscles of the ear, 

 pharynx, larynx, tongue, oesophagus, and those around the 

 anus and sexual organs. All the striated muscles in vertebrates 

 (except heart muscle) are voluntary. There are some excep- 

 tions, however, such as the muscles of the upper part of the 

 oesophagus, and the cremaster externus, which are not under 

 the control of the will. 



Histogenesis of Voluntary Striated Muscle. 



The voluntary muscle of the adult body is derived from the 

 myotomes of the embryo. In pigs' embryos 8 mm. long the 

 myotomes are flattened bodies composed of a dorsolateral 

 epithelium-like layer of cells, and a median mass of spindle- 



FIG. 63. 



Transverse section through the epithelial lamella of a myotome in the leg region of 

 an embryo pig 8 ram. long. (Bardeen.) a, dividing cells ; b, limiting capsule of external 

 layer; c, inner layer ; d, middle spindle-cell layer ; e, ectoderm. 



shaped and round cells. These have been described in detail 

 by Bardeen. The epithelial lamella (cutis plate) is composed 

 of three layers of columnar cells with fine fibres proceeding 



