TISSUES OF THE BODY. 



293 



Fig. 288. 



render visible the boundaries of the individual cells artificially (Aeby, 

 Ebertli , Sch weigger-Seidel) . 



In the other transversely striped muscles of the body it is the exception 

 to find branching fibres. 



REMARKS. The retiform connections of striped muscle fibres were described by 

 Leuckart and myself many years ago, and probably for the first time, as occurring 

 in arthropods, and noted later as of frequent occurrence among invertebrate animals. 

 In the year 1849 they were again brought to light by Koelliker, having been pre- 

 viously seen by Leeuwenhock. 



168. 



The fibres of striped muscle are arranged parallel to one another (with 

 exception of those of the heart), and ^ 



appear prismatic, owing to their mutual 

 contact (fig. 288, a). Their direction is 

 that of the long axis of the muscle. Be- 

 tween them is situated a very small quan- 

 tity of interstitial connective- tissue, in 

 which the nutrient capillaries (d) and 

 nerves of the part are contained. 



Several of these muscle fibres are usually 

 united to form a bundle varying in thick- 

 ness from 0'5 to 1 mm., and separated 

 from the surrounding bundles by a 

 stronger layer of connective- tissue. Such 

 primary fasciculi are then combined to form secondary, which present 

 themselves in very varying thickness. 



The connective-tissue envelope and uniting substance of muscle is 

 known under the name of " perimysium," two 

 kinds of which are recognised, namely, an external, 

 enveloping the whole structure, the perimysium 

 externum, and a continuation of the latter between 

 the fibres, the perimysium internum. 



Fat-cells (c) may also be met with in the connec- 

 tive-tissue of muscle, becoming more numerous in 

 obese bodies, or in muscles which have remained 

 long unused. Seen from the side, they are ar- 

 ranged in rows one after the other (fig. 289, b). 

 They may eventually interfere with the ability of 

 the fibres to perform their work. 



Bands of smooth muscle also, although they 

 seldom form such bulky muscles in the human 

 body as the first formation, are nevertheless put 

 together in a similar manner in bundles, wherever 

 they are crowded and collected in large numbers 

 together. On the other hand, contractile fibre- 

 cells appear frequently enough in the body in very 

 small aggregations, hidden and obscured by an excess of connective-tissue, 

 so that they can only be discovered amid the latter with difficulty. Con- 

 sequently, we may distinguish between pure and mixed unstriped muscle 

 (Koelliker). 



The vascularity of muscle is very considerable, and the arrangement of 

 its vessels characteristic (fig. 290). The arterial stems entering the 



Fig. 289. Human muscle 

 showing fat-cells, o, mus- 

 cular fibre; 6, rows of fat- 

 cells. 



