cxxiv MUSCULAR TISSUE. 



from different muscles, Kolliker infers that small muscles are destitute of 

 such vessels, and that the few which apparently issue from some of the 

 larger muscles, belong to the sheath and its larger subdivisions, and not to 

 the proper muscular tissue. 



Nerves. The nerves of a voluntary muscle are of considerable size. 

 Their branches pass between the fasciculi, and repeatedly unite with each 

 other in form of a plexus, which is for the most part confined to a small 

 part of the length of the muscle or muscular division in which it lies. 

 From one or more of such primary plexuses, nervous twigs proceed and 

 form finer plexuses composed of slender bundles, each containing not more 

 than two or three dark-bordered nerve-fibres, whence single fibres pass off 

 between the muscular fibres and divide into branches which are finally dis- 

 tributed to the tissue. The mode of final distribution will be described 

 with the general anatomy of the nerves. 



Nerves of small size accompany the branches of blood-vessels within 

 muscles, but do not reach the capillaries ; though destined for the vessels, 

 these nerves sometimes communicate with the proper muscular plexuses. 



Involuntary muscles. The involuntary muscular tissue differs from the 

 voluntary kind, not only in its want of subjection to the will, but also in 

 its external characters ; for whilst in many parts it appears in the form of 

 fibres, these, except in the heart and a few instances of less note, are un- 

 marked by the cross lines so characteristic of the striped fibres ; moreover, 

 they are in reality made up of elongated contractile cells cemented together 

 by some kind of uniting medium. 



Plain or unstriped muscular tissue (fig. LXIX.). This is generally of a pale 

 colour. The fibres are for the most part roundish or prismatic, but are 

 readily flattened in examination. Some are not above -y^^ of an inch 

 in diameter ; but the larger measure from -$-5-3-$ to -J^-Q (Ellis). Under 

 the microscope they have a peculiar soft aspect, without a strongly shaded 

 border ; and they are marked at short intervals with oblong corpuscles, 

 which give them a very characteristic appearance, especially after the appli- 

 cation of acetic acid, which renders the corpuscles much more conspicuous. 

 The substance of the fibres is translucent, but clouded or finely granular ; 

 and in the latter case the granules are sometimes arranged in longitudinal 

 lines. There is no sarcolemma. These fibres, as already said, are made up 

 of cells, named contractile fibre-cells, which were first distinguished as the 

 true elements of the tissue by Kolliker. The cells may form fibres, bundles, 

 and strata, or may be less regularly arranged, or mixed with other tissues 

 in greater or less proportion. They are of an oblong flattened shape (figs. LXX. 

 and LXXI), usually pointed at the ends, but sometimes abruptly truncated, 

 and varying greatly in length according to the part or organ in which they 

 are found. Some occur which are cleft or forked at one end. They mea- 

 sure for the most part from ^-l^ to ^-^ of an inch or more in length. Their 

 substance is finely granular and sometimes faintly striated, and, with few 

 exceptions, no distinction is visible between envelope and contents. Each 

 has a nucleus (a, a), rarely more than one, which is always elongated and 

 either oval or rod-shaped. Accordingly, the nuclei of the fibres above 

 described belong to the constituent cells. By macerating the tissue in nitric 

 acid diluted with four times its weight of water, the separation of the cells 

 is greatly facilitated. 



It is proper to state that a different view of the structure of the plain muscular 

 tissue is entertained by some authorities. Mr. Ellis, after a very extended inquiry, 



