Heart-muscle fibres in sec- 

 tion : the peripheral zone 

 is composed of radially-ar- 

 ranged groups (/) of muscle- 

 columns ; a zone (<r) of less 

 differentiated sarcoplasm 

 surrounds the nucleus. 



FIG. 80. 



THE MUSCULAR TISSUES. 67 



Sometimes, in preserved tissue, the position of the nucleus is occu- 

 pied by a clear vacuole. 



Ranvier has called attention to certain differences in the muscles 

 of the rabbit, describing two varieties the red or especially dark 

 (semitendinosus, soleus) and the white or pale 

 (adductor magnus). The red muscles are char- 

 acterized by slow response to electrical stimulus, 

 less regular transverse striation, greater dis- 

 tinctness of longitudinal markings, and great 

 number of round nuclei. 



The blood-vessels of striated muscle are 

 very numerous. The larger vessels, together 

 with the nerve-trunks and, less frequently, the 

 lymphatics, are contained within the perimy- 

 sium, where they give off numerous smaller 

 branches ; these, in turn, extend between the primitive bundles and 

 break up into extremely thin capillaries, which form a characteristic 

 rectangular-meshed net-work around the indi- 

 vidual muscle-fibres. The longer sides of the 

 meshes correspond with the axis of the fibre. 

 At various points along the course of these 

 vessels peculiar dilatations, or ampullae, occur, 

 the object of which is, probably, the relief of sud- 

 den temporary interference with the circulation 

 during muscular contractions. The relation be- 

 tween the capillary blood-vessels and the muscu- 

 lar fibres of the heart is very intimate ; in many 

 places the vessels lie embedded within or even en- 

 tirely surrounded by the muscular tissue (Meigs). 



Lymphatic vessels occur in striated muscle 

 in small numbers, but are entirely wanting in 

 many small muscles ; when distinct lymphatic 

 vessels do occur, they are confined to the larger 

 and looser masses of the perimysium (Kolliker). 



The nerves supplying the striated muscle 

 include the principal trunks which run within the perimysium, where 

 they subdivide into smaller groups of medullated fibres, in order to 

 reach the individual muscle-fibres ; these latter receive their nervous 

 supply at certain points only, the nerves passing to the muscle to 

 end in the special end- plates in the manner described more fully 

 in connection with the peripheral nerve-endings. 



The development of all varieties of muscular tissue is closely 

 related to the mesoderm, of which they are the direct descendants. 

 The plain or non-striated muscle is formed by the differentiation, 



Injected voluntary mus- 

 cle : the capillaries form 

 rectangular-meshed net- 

 works enclosing (he indi- 

 vidual fibres. 



