246 Growth and Histogenesis of Nerves 
From this latter branch nerve-fibrils are sent out in company with 
sheath-cells to each muscle-fibre. A sheath-cell becomes applied to the 
surface of the muscle-fibre, while the protoplasm of the latter in the 
vicinity of the sheath-cell becomes granular and nuclei collect about the 
granular area. At the time of the formation of the end-plate, the 
muscle-fibre possesses both peripheral and central nuclei. I have else- 
where (1900) given pictures of cross-sections of muscle-fibres which 
seem to show a wandering of central nuclei toward the surface of the 
cell. The nuclei which collect about the granular area of the muscle- 
fibre seem to arise from the surface nuclei. They represent probably 
the nuclei of the sole of the adult muscle-plate while the nucleus of 
the cell which accompanies the nerve-fibre to the muscle-fibre, probably 
represents a nucleus of the sheath, or possibly a nucleus of arborization. 
Fig. 10 shows an early stage in the union of nerve-fibres and muscle-cells. 
Fig. 10. Fie. 11. 
Fig. 10. An early stage in the union of nerve and muscle-fibres. From a gold- 
chloride specimen of the rectus muscle of a pig 19 cm. long. 720 diam. For the 
sake of contrast the surface nuclei are represented very much darker than they ap- 
pear in the specimen. 
Fig. 11. Nerve, nerve-ending, and sarcolemma from a portion of the rectus 
muscle of afrog. 720 diam. 
Union of nerve-fibres and muscle-cells does not begin to be common 
until the embryo has reached a length of 15 em., and it continues for a, 
considerable period after this time. So far as I have been able to 
determine, a definite sarcolemma forms after the nerve-fibre and sheath- 
cell have joined the muscle-cell. By the digestion of specimens hard- 
ened in osmic acid I have been able to isolate delicate sarcolemmata 
from muscle-cells of the rectus of pig embryos 20 em. long, but not from 
younger embryos. ‘This valuable digestion method of Chittenden also 
enables one to show the relation of the sarcolemma to the sheath of 
——S 
