460 KED AND PALE MUSCLES. 



suddenly or by means of a small swelling a view confirmed by Rauber. The 

 existence of sensory nerves in muscles is also proved by the fact that stimulation 

 of the central end of a motor nerve, e.g., the phrenic, causes increase of the blood- 

 pressure and dilatation of the pupil {Asp, Kowalewsky, Nmvrocki), as well as by the 

 fact that when they are inflamed they are painful. They of course do not de- 

 generate after section of the anterior root of the spinal nerves. 



Red and Pale Muscles. In many fishes A (skate, plaice, herring, mackerel) {W. Stirling), 

 birds, and mammals (rabbits), there are two kinds of striped muscle (Krause), differing in 

 colour, histological structure (Eanvier), and physiological properties (Kronecker and Stirling). 

 Some are red," e.g., the soleus and semitendinosus of the rabbit, and others "pale," e.g., 

 the adductor magnus. In the pale muscles the transverse striation is less regular, and their 

 nuclei fewer than in the red muscles (Hanvier) ; they contain less glycogen and myosin. [W. 

 Stirling finds that the red muscles in many fishes, e.g., the mackerel, contain granules of oil, 

 and present all the appearance of, muscle in a state of fatty degeneration, while the pale 

 muscles, lying side by side, contain no fatty granules. ] 



Julius Arnold found in human muscles an extensive distribution of pale fibres amongst 

 the red ones, and indeed in the same muscle in the frog and mammals, red and pale fibres 

 occur together, in fact this is the case in almost every muscle (Grutzncr). 



[Spectrum. The red colour of the ordinary skeletal muscle is due to haemoglobin in the sarcous 

 substauce (Kiihne). This is proved by the fact that the colour is retained after all the blood 

 is washed out of the vessels, when a thin muscle still sbows the absorption-bands of haemo- 

 globin when examined with the spectroscope. 1 



[Myo-hsematin. MacMunn points out that although most voluntary muscles owe their 

 colour to haemoglobin, it is accompanied by myo-htematin in most cases, and sometimes entirely 

 replaced by it. Myo-hrematiu is found in the heart of vertebrates, in the papillary muscles of 

 the human heart, and in abundance in the pectoral muscles of pigeons, and in some muscles 

 of vertebrates and invertebrates, e.g., certain beetles (Hydrophilus, Dytiscus), the common fly, 

 and other insects, spiders, crustaceans, and molluscs.] 



Muscular Fibres of the Heart. The mammalian cardiac muscle has certain peculiarities 

 already mentioned ( 43) : (1) It is striped, but it is involuntary ; (2) it has no sarcolemma ; 

 (3) its fibres branch and anastomose ; (4) the transverse striation is not so distinct, and it is 

 sometimes striated longitudinally ; (5) the nucleus is placed in the centre of each cell (see 

 43). [The cardiac muscle,- viewed from a physiological point of view, stands midway between 

 striped and unstriped muscle. Its contraction occurs slowly and lasts for a long time (p. 86), 

 while, although it is transversely striped, it is involuntary.] 



[Purkinje's Fibres. These fibres, which form a plexus of greyish fibres under the endo- 

 cardium of the heart of ruminants, have been described already (fig. 28) ; the cells have, as it 

 were, advanced only to a certain stage of development ( 46).] 



Development. Each muscular fibre is developed from a uni-nucleated cell of the mesoblast, 

 which elongates into the form of a spindle. As the cell elongates, the nuclei multiply. The 

 superficial or parietal part of the cell-substance shows transverse markings (fig. 302, 7), while 

 the nuclei with a small amount of protoplasm are continuous along the axis of the fibre, where 

 they remain in some animals, but in man they pass to the surface where they come to lie under 

 the sarcolemma. The muscles of Ithe young are smaller and have fewer fibres than those of 

 adults {Budge). In developing muscle, the number of fibres is increased by the proliferation 

 of the muscle-corpuscles, which form new fibres. 



Striped muscle, besides occurring in the corresponding organs of vertebrata, occurs in the 

 iris and choroid of birds. The arthropoda have only striped muscle, the molluscs, worms, 

 and echinoderms chiefly smooth muscles ; in the latter are muscles with double oblique striation 

 {Schwalbc). According to Paneth, in old individuals separate cells with aggregation of con- 

 tractile substance so-called Sarcoplasts unite to form new muscular fibres. Sig. Mayer regards 

 these structures as retrogressive structures, and he calls them Sarcolytes ( 103, II.). 



2. Non- Striped Muscle. [Distribution. It occurs very widely distributed in the body, in 

 the muscular coat of the lower half of the human oesophagus, stomach, small and large intestine, 

 muscularis muscosae of the intestinal tract, in the arteries, veins, and lymphatics, posterior part 

 of the trachea, bronchi, infundibula of the lung, muscular coat of the ureter, bladder, urethra, 

 vas deferens, vesiculae seminales, and prostate ; corpora cavernosa and spongiosa penis, ovary, 

 Fallopian tube, uterus, skin, ciliary muscle, iris, upper eyelid, spleen and capsule of lymphatic 

 glands, tunica dartos of the scrotum, gall-bladder, in ducts of glands, and in some other 

 situations.] 



Structure. Smooth muscular fibres consist of fusiform or spindle-shaped elongated cells, 

 with their ends either tapering to fine points or divided (fig. 312). These contractile fibre-cells 

 may be isolated by steeping a piece of the tissue in a 30 per cent, solution of caustic potash, or 

 a strong solution of nitric acid. They are 45 to 30 fi [^ to T ^ in.] in length, and 4 to 10 p 

 [tttsW to tsVs in.] in breadth. Each cell contains a solid oval elongated nucleus, which may 



