Introduction To Muscles Introduction to animal muscles with special reference to humans

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Muscles are the moving organs of the animal frame. They constitute the great bulk of the body by their size and number, and they bestow form and symmetry to the body. In the limbs they are situated around the bones, which they invest and defend, while they form to some of the joints a principal protection. In the trunk they are spread out to enclose cavities, and constitute a defensive wall capable of yielding to internal pressure, and again returning to its original form.Their color is deep red which is characteristic of flesh, and their form is variously modified, to execute the varied range of movements which are required from them.Muscle is composed of a number of parallel fibers placed side by side, and supported and held together by a delicate web of cellular tissue ; so, that if it were possible to remove the muscular substance, we will get a beautiful cellular framework, possessing the exact form and size of the muscle without its color and solidity. Towards the extremity of the organ the muscular fiber ceases, and the cellular structure becomes aggregated and modified, so as to constitute those fibers and cords by which the muscle is tied to the surface of bone called the tendons. Almost every muscle in the body is connected with bone, either by tendinous fibers or by an aggregation of those fibers constituting a tendon and the union is so firm that under extreme violence the bone itself breaks but the tendon do not separate from its attachment. In the broad muscles the tendon is spread so as to form an expansion, called aponeurosis.Muscles present various modifications in the arrangement of their fibers in relation to their tendinous structure. Sometimes they are completely longitudinal, and terminate at each extremity in tendon, the entire muscle being fusiform in its shape as in the case of biceps muscle. In other situations they are disposed like the rays of a fan, converging to a tendinous point, as the temporal and pectoral muscles. Sometimes they are converging like the plumes of a pen to one side of a tendon which runs the whole length of the muscle, as in the peronei. Sometimes they are bipenniform, converging to both sides of the tendon.