MUSCLE TISSUE 121 



fusing. The following is the scheme of structure and the nomenclature accord- 

 ing to Heidenhain (Fig. 64). 



The older terms muscle cell for the smooth muscle cell, and muscle fibre for 

 the analogous multinuclcar element of striated muscle are retained, also Apathy's 

 myofibril for the ultimate fibrilla, Kolliker's muscle column for the smallest bun- 

 dles of fibrils, and sarcoplasm for interfibrillar substance. 



The muscle fibre is subdivided into a series of segments by transverse discs 

 which completely cross the fibre, involving both fibrilla; and sarcoplasm and 

 are attached to the sarcolemma. This disc (ground membrane — membrane of 

 Krause,) Heidenhain designates the telophragma (Z). That part of a fibre which 

 hes between two telophragmata is an inokomma. The middle of each inokom- 

 ma is crossed by a disc (Hensen's membrane) which also involves both fibrillae 



Fig. 6,3. — Semidiagrammatic Drawing of Transv^erse Section of a Voluntary Muscle 

 Fibre, showing Sarcolemma; sarcoplasm separating fibrils into bundles, each bundle 

 constituting a muscle column of Kolliker and the appearance of its cross-cut end being 

 Cohnheim's field, a, Sarcoplasm; b, Cohnheim's fields; c, sarcolemma. 



and sarcoplasm and is attached to the sarcolemma. This membrane having 

 apparently the same structure as the telophragma is designated the mesophragma 

 (M). The mid-portion of the inokomma consists of anisotropic substance 

 (Q), the ends of isotropic (J). That portion of Q which lies on either side of M is 

 lighter than the rest of Q and is designated Qh (h = hell = clear) . That portion of 

 J which lies close on either side of Z is darker than the rest of J and is designated 

 Jd (d = dicht = thick). In the sarcoplasm between the fibrillae are granules; those 

 in J are arranged in a regular row and are known as J-granules, those in Q are 

 more irregularly placed and are known as Q-granules. In Fig. 64 are also shown 

 the "cross-fibre-nets" which are brought out by metallic impregnation and 

 which possibly represent intracellular canals. 



I Two varieties of striated voluntary muscle fibres are distinguished, 

 white fibres and red fibres. The difference betv^een the two is due 

 to the amount of sarcoplasm — the red fibres being rich in sarcoplasm, 

 the white fibres poor. Red fibres contract less rapidly than white, 

 but are less easily fatigued. In man white fibres are in the large 

 majority, red fibres never occurring alone, but mingled with white 

 fibres in some of the more active muscles, such as those of respiration 



