THE STRUCTURE OF THE MOTOR ORGANS 85 



Certain insects' muscles happen to be so constituted that the 

 sarcostyles can be separated one from another and isolated ones 

 gotten under the field of the microscope for study. When exam- 

 ined thus singly and free from surrounding media which distort 

 the view, these sarcostyles are seen to be tiny cylinders divided at 

 regular intervals by transverse partitions, made, apparently, of 

 delicate membrane. Many biologists think it likely that the sar- 

 costyles of ordinary skeletal muscle have really this same struc- 

 ture; that the position of the transverse membranes is indicated by 

 faint dark lines in the middle of the light bands and that the ap 

 pearance of light and dim bands of nearly equal width is an optical 



FIG. 43. The muscular coat of the stomach. 



illusion due to the unfavorable conditions of observation. Since 

 the fiber as a whole contains many sarcostyles and since the cross 

 striations are regular throughout the entire fiber it follows that all 

 the sarcostyles of any fiber must have their partitions at corre- 

 sponding levels. The sarcostyles are probably kept in place by an 

 interfibrillar network of some sort. 



The blood-vessels and nerve-fibers supplied to the skeletal 

 muscles are numerous. - The larger blood-vessels run in the coarser 

 partitions of the connective tissue lying between the fasciculi and 

 give off fine branches which form a network between the individual 

 fibers but never penetrate the sarcolemma. 



Connected with each muscle-fiber is a nerve-fiber. The central 

 core of the nerve-fiber ends in an oval expansion (end plate) which 



