MUSCULAR TISSUE. 143 



Transversely striated muscle-fibers are usually unbranched. 

 The muscle-fibers of the tongue and of the ocular muscles do, how- 

 ever, show occasionally communicating branches ; the same are 

 but very rarely seen in other muscles. In regions where striated 

 muscle-fibers terminate under the epithelium, as in the tongue and 

 in the skin of the face, the end of the fiber terminating under the 

 epithelium is often very much branched ; the cross-striation and 

 nuclei may be observed in the finest branches. (Fig. 101.) 



Each muscle-fiber is surrounded by a thin connective-tissue en- 

 velope, the endoinysiuin,vr\\\c\i binds them into primary and second- 

 ary bundles, the muscle-fasciculi. These are surrounded by a 

 denser sheath of similar character, the perimysium. The muscle is 

 made up of numerous fasciculi, all bound together by a thicker con- 

 nective-tissue covering, the epimysium. (Fig 102.) 



Blood-vessels are very numerous in transversely striated mus- 



-- Nucleus. 



Contractile 

 substance. 



Contractile 



substance. 



Nucleus. 



Fig. 104. Fig. 105. 



Longitudinal and cross-section of muscle-fibers from the human myocardium, hard- 

 ened in alcohol ; X 640. The muscle cells in the longitudinal section are not sharply 

 defined from each other, and appear as polynuclear fibers blending with each other. 

 Between them lie, here and there, connective-tissue nuclei. 



cular tissue. One or several arteries enter each muscle and form 

 superficial and deeper plexuses by anastomosis. In these plexuses 

 the arteries are accompanied by veins. On reaching the perimysium 

 the arteries give off terminal branches which run transversely over 

 the muscle fasciculi, at quite regular intervals. From these branches 

 precapillaries and capillaries are given off which have a course 

 which is in general parallel to the muscle-fibers ; these capillaries 

 anastomose frequently and collect to form small veins, which are 

 situated between the terminal arterial branches, the terminal arterial 

 and venous branches thus alternating in such a way that one venous 

 branch is situated between two arterial branches or vice versa. The 

 veins, even the smallest, are provided with valves (Spalteholz). 



