MUSCULAR TISSUE. 55 



Bowman), connected together like a string of beads. Closer examination, 

 however, shows that the elementary particles are little masses of pellucid 

 substance, having a rectangular outline, and appearing dark in the centre. 

 These appearances would favor the suggestion that the elementary particles 

 of which the fibrils are composed are possibly nucleated cells, cohering in a 

 linear series, the transverse marks between them corresponding to their line 

 of junction. Kolliker, however, considers " the sarcous elements as artificial 

 products, occasioned by the breaking up of the fibril at the parts where they 

 are thinner." 



This form of muscular fibre composes the whole of the voluntary muscles, 

 all the muscles of the ear, those of the larynx, pharynx, tongue, the upper 

 half of the oesophagus, the heart, and the walls of the large veins at the point 

 where they open into it. 



The fibres of the heart, however, differ in several particulars from those of 

 other striped muscles. They are smaller by about one -third, and their trans- 

 verse stria3 are by no means so distinct. Fat-cells are also often found in them 

 to a large extent, even apart from any obvious disease of the organ. They 

 break up much more readily into their smallest elements. There is also much 

 less (if any) connective tissue separating the bundles of fibres ; and Kolliker 

 has described and figured the ultimate fibres as anastomosing with each other. 



The Unslriped Muscle, or Muscle of Inorganic Life, is found in the walls of 

 the hollow viscera, viz., the lower half of the oesophagus and the whole of the 

 remainder of the gastro-intestinal tube ; in the trachea and bronchi ; in the 

 gall-bladder and ductus communis choledochus ; in the pelvis and calices of 

 the kidney, the ureters, bladder, and urethra; in the female sexual organs, viz., 

 the Fallopian tubes, the uterus (enormously developed in pregnancy), the 

 vagina, the broad ligaments, and the erectile tissue of the clitoris ; in the .male 

 sexual organs, viz., the dartos scroti, the vas deferens, and epididymis, the 

 vesiculas seminales, the prostate gland and the corpora cavernosa; 1 in the 

 ducts of certain glands, as in Wharton's duct; in the capsule and trabeculae 

 of the spleen ; in the arteries, veins, and lymphatics ; in the iris ; and in the 

 skin. 



The fibres of inorganic muscle form flattened bands, interlacing in various 

 directions, and which, when viewed without reagents appear nearly homo- 

 geneous, though if the organ from which the fibres are taken has been mace- 

 rated previously for some time in dilute acid, the nuclei can be perceived. 

 Even in fresh fibres the nuclei are occasionally visible. 



In many situations these fibres, by prolonged immersion in chromic or nitric 

 acid, can be resolved into the elementary contractile fibre-cells, of which 

 Kolliker has shown that they really consist; and in some parts, as in the 

 arteries and in the skin, such fibre-cells are found single. They are elongated, 

 their length about ten to fifteen times their breadth (.02"' to 0.4'" in length, 

 .002'" to .003"' in breadth, according to Kolliker), consisting of a spindle- 

 shaped, homogeneous-looking, fibre-cell, in which a rod shaped nucleus is 

 faintly visible. Acetic acid dissolves out the granular contents of the cell, and 

 brings the nucleus clearly into view. 



The unstriped muscle, as a rule, is not under the influence of the will, nor 

 is the contraction rapid and involving the whole muscle, as is the case with 

 the muscles of animal life. The membranes which are composed of the un- 

 striped muscle slowly contract in a part of their extent, generally under the 

 influence of mechanical stimulus, as that of distension or of cold, and then the 

 contracted part slowly relaxes, while another portion of the membrane takes 

 up the contraction. This peculiarity of action is most strongly marked in the 

 intestines, constituting their vermicular motion. 



In chemical composition, the muscular fibres of both forms consist mainly of 



1 Kolliker describes muscular fibres also in the tunica vajnnalis testis. 



