232 



THE MUSCLES. 



B, ULTIMATE FIBRIL OF 

 MUSCLE (ACCORDING 

 TO bowman). 



0, Muscular fibre more 

 highly magiiiried, its 

 myolemma being so 

 thin and transparent 

 as to allow the ulti- 

 mate fibrillae to be 

 seen. 



in the fresh muscles of insects ; in the Mgher animals, this disassociation into 

 parallel fibrillae is generally only possible in muscles subjected to the action of 

 certain reagents. Other reagents favour the breaking up of the fibre into super- 

 posed discs ; hence it has been concluded that the fundamental element of the 

 primitive muscular fibre was not a fibril, but a discoid segment of fibrillae, to which 

 Bowman gave the name of sarcous elements (Fig. 148). 



Bowman considered that the transverse striag represent the lines of union of 

 the sarcous elements. But nowadays the striation of the fibre is explained by 

 the striation of the primitive contractile cylinders ; in 

 fact, each of these is divisible into a series of thick, dark- 

 coloured, contractile discs, joined by bright l)ands which 

 play the part of a tissue framework in the cylinder. In 

 the majority of Mammals, the thick discs are traversed in 

 their middle by a pale streak named the intermediate band 

 or streak of Hensen ; in the middle of each bright band is 

 a thin disc dividing it into two parts. In the Invertebrata 

 the situation is more complicated, as is seen in Fig. 147. 

 Ranvier has remarked that there is, in the Skate and 

 Rabbit, pale and dark striped muscles. The pale muscles 

 are recognized by the predominance of the transverse 

 striation and the rarity of nuclei ; while the fibres of the 

 dark muscles present, on the contrary, a great number of 

 nuclei and prevailing longitudinal striation. Layocat and 

 Arloing have examined these differences in the muscular 

 apparatus of some Fishes, Birds (Fowls, Guinea-fowls), 

 and domestic Mammals (Dog, Ox, Horse), and their 

 observations confirm those of Ranvier, apart from some secondary differences 

 special to the varied species on which they made their investigations. 



The muscular fibres are united parallel to each other to form secondary 

 fasciculi, which are surrounded by a connective sheath — the internal perimysium. 

 The secondary fasciculi are laid together to constitute more voluminous fasciculi, 



which, in their turn, form the entire 

 muscle. The connective sheath enveloping 

 the muscle is named the external perimy- 

 sium. 



B. Tendons and Aponeuroses. — 

 The tendons are white, nacreous, round, 

 or flattened cords fixed to the extremities 

 of the long muscles. They are composed 

 of fasciculi of connective-tissue fibres, 

 covered by a layer of flat cells ; they have a parallel direction, and are united to 

 one another by loose connective-tissue sheaths. 



The elementary fibres succeed the primitive striped fibres ; the latter terminate 

 in rounded extremities, and are fused to the fibrous fasciculi — hollowed into a kind 

 of cup — by an intermediate and very solid amorphous substance. 



The aponeuroses belong almost exclusively to the wide muscles ; they are 

 formed of several planes of parallel fibres which are not intercrossed in their 

 middle part ; at their superficies, however, the fil)rous fasciculi are matted together 

 in a more or less inextricable manner. 



It is very interesting to study the mode of union of the muscular fibres with 



Fis. U»). 



MUSCULAR FIBRE BROKION ACROSS, SHOWING 

 THE UNTORN SARCOLEMMA CONNECTING 

 THE FRAGMENTS. 



