STEUCTURE OF THE VOLUNTARY MUSCLES. 531 



present the striae and all the anatomical characteristics of the primitive fasciculi, and that 

 by far the most natural and easy mode of separation of these fasciculi is in a longi- 

 tudinal direction. The question of adopting one or the other of these views is not of 

 very great physiological importance. * 



Fibrous and Adipose Tissue in the Voluntary Muscles. The structure of the mus- 

 cles strikingly illustrates the relations between the principal and the accessory anatomi- 

 cal elements of tissues. The characteristic, or principal element is, of course, the mus- 

 cular fibre or fibrilla ; but we also find in the substance of the muscles certain anatomi- 

 cal elements, not peculiar to the muscles, and merely accessory in their function, but 

 none the less necessary to their proper constitution. For example, every muscle is com- 

 posed of a number of primitive fasciculi ; but these are gathered into secondary bundles, 

 which in turn are collected into bundles of greater and greater size, until, finally, the 

 whole muscle is enveloped in its sheath and is penetrated by a fibrous connective sub- 

 stance. We find, probably, in the muscles, the best illustration of the structure of what 

 is known as the connective tissue. 



Connective Tissue. We have already had occasion to refer to certain of the elements 

 of connective tissue, more especially the inelastic and elastic fibres. In this connection, 

 we shall treat specially of the connective tissue of the muscles ; but our description will 

 answer for almost all situations in which fibrous tissue exists merely for the purpose of 

 holding parts together. In the muscles, we have a membrane holding a number of the 

 primitive fasciculi into secondary bundles. This is known as the perimysium. The 

 fibrous membranes that connect together these secondary bundles with their contents 

 are enclosed in a sheath enveloping the whole muscle, sometimes called the external 

 perimysium. The peculiarity of these membranes, and their distinction from the sar- 

 colemma, are that they have a fibrous structure and are connected together throughout the 

 muscle, while the tubes forming the sarcolemma are structureless, and each one is dis- 

 tinct. 



FIG. 15G. Fibres of tendon of the human subject. (Rollett.) 



The name now most generally adopted for the tissue under consideration is connec- 

 tive tissue. It has been called cellular, areolar, or fibrous, but most of these names were 

 given to it without a clear idea of its structure. Its principal anatomical element is a 

 fibre of excessive, almost immeasurable, tenuity, wavy, and with a single contour. These 

 fibres are connected into bundles of very variable size and are held together by an 

 adhesive amorphous substance. The wavy lines that mark the bundles of fibres give 

 them a very characteristic appearance. 



The direction and arrangement of the fibres in the various tissues present marked 



