Chap. V.] 



GENERAL HISTOLOGY. 



73 



darker substance. The lighter bands are the septal zones (Fig. 

 26, iii.), the darker the interseptal zones. Within the latter very 

 delicate longitudinal striations may be made out. In the midst 

 of the septal zone is a delicate dotted line, the septal line. The 

 space between the septal lines is termed a muscle segment. 



In growing muscle spindle-shaped cells are active in the 

 formation of muscular fibres, just as spindle-shaped or branched 

 cells are active in the formation of fibrous connective tissue. 



Fig. 26, i., shows a muscular fibre of the frog, the elongated 

 black spots being the muscle corpuscles. Where the fibre is 

 twisted the sarcolemma becomes obvious. 26, iii., is a 



Fio. 20. MUSCLE AND NERVE. 



i. Striped muscle, ii. Unstriped muscle cells, iii. Striped muscle under 

 highest power. . Septal line. &. Septal zone. c. Interseptal zone. iv. Trans- 

 verse section of sciatic nerve of rabbit, v. A portion more highly magnified, 

 vi. Nerve fibre, after chloroform, vii. Nerve fibre with primary node, after 

 osmic acid. viii. Nerve fibre with nerve corpusle, after osmic. ix. Nerve 

 cell from sympathetic ganglion of frog. x. Unipolar nerve cell. xi. Multi- 

 polar nerve cell. xii. Section of spinal cord from cervical region of kitten. 



diagram to show : a. septal line, b. septal zone, <'. interseptal 

 zone. 



(b.) Unstriped. Involuntary unstriped muscle occurs in the 

 walls of the alimentary canal, of the bladder, and of the blood- 

 vessels. The fibres are moderately elongated, flattened, and 

 tapering at the ends (fusiform). Each has a readily-stained 

 nucleus (26, ii.), which may also be made obvious by treatment 



