118 



MUSCULAR TISSUE. 



Nerves of small size accompany the branches of blood-vessela witliiii 

 muscles ; though destined for the vessels, these nerves are said some- 

 times to communicate with the proper muscular plexuses. 



INVOLTJNTART 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 unmarked 



by the cross lines so character- 

 Fig- 76. istic of the striped fibres ; more- 

 over, they are in reality made 

 up of elongated contractile cells 

 cemented together by some 

 kind of uniting medium. 



Plain 01* unstriped mus- 

 cular tissue. — This, as has 

 just been remarked, is made 

 up of cells, named contractile 

 fibre-cells, which were first dis- 

 tinguished as the true elements 

 of the tissue by Kolliker. The 

 cells may form fibrous bundles^ 

 and strata, or may be less re- 

 gularly arranged, or mixed with 

 other tissues in greater or less 

 proportion. They are of an 

 elongated fusiform shape (figs. 

 76 and 77), usually pointed at 

 the ends, but sometimes ab- 

 ruptly truncated, and are round- 

 ish or prismatic in transverse 

 section. The cells vary greatly 

 in length according to the part 

 or organ in which they are 

 found. Some occur whicli are 

 cleft or forked at one end. 

 Their substance is finely granu- 

 lar and commonly exhibits a 

 faint longitudinal striation. It 

 has a smooth soft aspect, and 

 presents no indication of an 

 envelope. Each has a nucleus 

 {a, a), rarely more than one, 

 Avhich is always elongated and 

 either oval or rod-sliaped. 

 Towards each end of the nu- 

 cleus the substance of the cell 

 usually contains a few larger granules arranged in linear series. 



The plain muscular tissue is for the most part disposed between the 

 coats of the memln-anous viscera, as the stomach, intestines, and bladder, 

 in the parietes of the air-tubes, excretory ducts of glands, and the like. 



M 



Fig. 77. — Mu.scuLAR Fibre-Cells 

 FROM Human Arteries, magnified 

 350 DIAMETERS (KiJlHker). 



a, natural state ; i, treated witli 

 acetic acid. 



Fig. 7(). — Muscular Firre-Cell from the 

 Muscular Coat of the Small Intestine, 

 MAGNIFIED (Kijlliker). 



