454 



STRUCTURE AND ARRANGEMENT OF MUSCLES. 



trating the fibres, which, however, they cross (fig. 307). In a contracted muscle the capil- 

 laries may be slightly sinuous in their course, bnt when a muscle is on the stretch these curves 

 disappear The capillaries lie in the endomysium, and near them are lymphatics]. Each 

 IS -fibre receives a nerve-fibre. [Where found. -Striped muscular fibres occur in the 

 Skeletal muscles, heart, diaphragm, pharynx, upper part of oesophagus, muscles of the middle 

 ear and pinna, the true sphincter of the urethra and external anal sphincter] 



Amuicular fibre (fig. 302, 1) is a more or less cylindrical or polygonal fibre 11 to 6 / /* 

 rt to r^ in.] in diameter, and never longer than 3 to 4 centimetres [1 to 1J in] Within 

 short musdes, c,j., stapedius, tensor tympani, or the short muse es of a frog the fibres are as 

 muscle itself ; within longer muscles, however, the individual fibres are pointed, 



long as th 



Fig. 302. 

 Histology of muscular tissue. 1, Diagram of part of a striped muscular fibre ; S, sarcolemma ; 

 Q, transverse stripes ; F, fibrillar ; K, the muscle nuclei ; N, a nerve-fibre entering it 

 with a, its axis cylinder and Kiihne's motorial end-plate, c, seen in profile ; 2, transverse 

 section of part of a muscular fibre, showing Cohnheim's areas, c ; 3, isolated muscular fibrillar ; 

 4, part of an insect's muscle greatly magnified ; a Krause-Amiei's line limiting the 

 muscular cases ; b, the doubly-refractive substance ; c, Hensen's disc ; d, the singly-refrac- 

 tive substance ; 5, fibres cleaving transversely into discs ; 6, muscular fibre from the heart 

 of a frog ; 7, development of a striped muscle from a human foetus at the third month ; 

 8, 9, muscular fibres.of the heart ; c, capillaries ; b, connective-tissue corpuscles ; 10, smooth 

 muscular fibres ; 11, transverse section of smooth muscular fibres. 



and are united obliquely by cement-substance with a similar bevelled or pointed end of another 

 fibre lying in the same direction. Muscular fibres may be isolated by maceration in nitric acid 

 with excess of potassic chlorate or by a 36 per cent, solution of caustic potash. 

 [Each muscular fibre consists of the following parts : 



1. Sarcolemma, an elastic sheath, with transverse partitions, stretching across the fibre'at 



regular intervals the mernbrane of Krausc ; 



2. The included sarcous substance ; 



3. The nuclei or muscle corpuscles. ] 



