

VESSELS AND NERVES OF MUSCLES. 203 



of the heart ; whose walls are composed of a similar tissue, for some 

 time after its rhythmical movements have become established. 



340. We have seen that the Muscular tissue, properly so called, is 

 as extra-vascular as cartilage or dentine ; for its fibres are not pene- 

 trated by vessels ; and the nutriment required for the growth of its con- 

 tained matter is drawn by absorption through the myolemma. But the 

 substance of Muscle is extremely vascular ; the capillary vessels being 

 distributed in nearly parallel lines, in the minute interspaces between 

 the fibres (Fig. 67) ; so that it is probable that there is no fibre, which 



Fig. 67. 



Capillary network of Muscle. 



is not in close relation with a capillary. Hence there is every provi- 

 sion for the active nutrition of this tissue ; the arterial circulation bring- 

 ing the materials for its growth and renovation ; whilst the venous con- 

 veys away the products of the waste or disintegration, which is consequent 

 upon its active exercise. The supply of blood is not merely requisite 

 for the nutrition of the muscular tissue ; but it also affords a condition 

 which is requisite for its action. This condition is oxygen. It is not 

 enough that blood should circulate through the muscles ; for that blood, 

 to exercise any beneficial influence, must be arterialized. Consequently 

 the muscles of warm-blooded animals soon lose their contractile power, 

 after the supply of arterial blood has been suspended, either by the ces- 

 sation of the circulation, or by the want of aeration of the blood ; but 

 those of cold-blooded animals preserve their properties .for a much longer 

 period, in accordance with the general principle formerly stated, that, 

 the lower the usual amount of vital energy, the longer is its persistence, 

 after the withdrawal of the conditions on which it is dependent. 



341. The Muscles of Animal Life are, of all the tissues except the 

 Skin, the most copiously supplied with Nerves. These, like the blood- 

 vessels, lie on the outside of the Myolemma of each fibre ; and their 

 influence must consequently be exerted through 7 it. The arrangement 

 of these nerves is shown in the succeeding figure. Their ultimate fibres 

 or tubes cannot be said to terminate anywhere in the muscular substance ; 

 for after issuing from the trunks, they form a series of loops, which 

 either return to the same trunk, or join an adjacent one (Fig. 68). The 

 occasional appearance of a termination to a nervous fibril is usually 

 caused by its dipping down between the muscular fibres, to pass towards 

 another stratum ; but it appears from recent inquiries to be sometimes 

 due to a subdivision of the central axis into a brush-like group of minute 

 fibrillse, which. form a yet minuter plexus around the muscular fibres.- 

 The non-striated muscles, however, are very sparingly supplied with 



