INVOLUNTARY MUSCLE. 



61 



- Nucleus. 

 Protoplasm. 



He calls attention to the similarity of the movements of the ameba, 

 muscle, and cilia. 



Muscles are well supplied with blood-vessels, which run 

 lengthwise of the muscle with transverse branches ; they do not 

 penetrate the sarcolemma. The motor nerves of striated muscle 

 terminate in motor end-organs, and the sensory nerves in muscle- 

 spindles, which are further referred to in the discussion of Nerve- 

 endings (p. 64). Besides the muscle- 

 fibers, muscles contain connective tissue 

 with some fat. 



Striated muscle is found in all the 

 muscles of the body which are attached 

 to bone, and is sometimes described un- 

 der the name skeletal muscle. Although 

 this variety is said to be voluntary, it is 

 not in all places under control of the 

 will, as, for instance, in the pharynx, 

 esophagus, and the internal ear. 



Development of Striated Muscular 

 Tissue. Embryonic cells of the meso- 

 blast become elongated, and the nuclei 

 form long fibers, which later become 

 striated ; some of the nuclei remain 

 beneath the sarcolemma as the nuclei 

 of the muscle. 



Cardiac Muscle(F\g. 54). The mus- 

 cle of which the heart consists differs 

 from that just described in having its 

 striae less marked, in being without sar- 

 colemma, and in the fact that its fibers 

 are short, each possessing a nucleus, and 

 that they branch and join the fiber- 

 cells contiguous to them. 



The nerves supplying cardiac muscle 

 end in plexuses or networks. 



Involuntary Muscle (Fig. 57). 

 This is also called plain and non-striated. 

 It consists of flat, fusiform cells, contrac- 

 tile fiber-cells, having lengths varying 



considerably, each possessing a nucleus and one or two nucleoli, 

 and having longitudinal striae. The cells are joined together by 

 means of an intercellular material. 



Involuntary muscular tissue is widely disseminated over the 

 body ; it is found in the following locations : esophagus, muscular 

 and mucous coats of the alimentary canal, bladder, ureter, uterus, 

 Fallopian tubes, spleen, ciliary muscle, iris, ducts of glands, arte- 



i 



FIG. 57. Smooth muscle- 

 cells from the intestine of a 

 cat : in 1, isolated ; in 2 and 3, 

 in cross-section; X300. At a 

 the cell is cut in the plane of 

 the nucleus ; at c, in the neigh- 

 borhood of the pointed end. 

 In 3 (from Barfurth) is seen 

 the manner in which neigh- 

 boring cells are joined to one 

 another by intercellular bridges 

 (Bohm and Davidoff). 



