153. In the description of a muscle, its attachments are expressed by the terms "origin" and "insertion." The term _origin_ is generally applied to the more fixed or central attachment, or to the point toward which motion is directed; while _insertion_ is assigned to the more movable point, or to that most distant from the centre. The middle, fleshy portion is called the "belly," or "swell." The color of a muscle is red in warm-blooded fish and animals; and each fibre is supplied with arteries, veins, lymphatics, and both sensitive and motor nervous filaments. 154. The FASCIA is of various extent and thickness, distributed through the different regions of the body, for the purpose of investing and protecting the softer and more delicate organs. An instance is seen in the membrane which envelopes a leg of beef, and which is observed on the edges of the slices when it is cut for broiling. When freshly exposed, it is brilliant in appearance, tough, and inelastic. In the limbs it forms distinct sheaths to all the muscles. 155. This tendinous membrane assists the muscles in their action, by keeping up a tonic pressure on their surface. It aids materially in the circulation of the fluids, in opposition to the laws of gravity. In the palm of the hand and sole of the foot, it is a powerful protection to the structures that enter into the formation of these parts. In all parts of the system, the separate muscles are not only invested by fascia, but they are arranged in layers, one over another. The sheath of each muscle is loosely connected with another, by the cellular membrane. -=-=-=-=-=-=-=-=-=-=-=-= 153. What is meant by the origin of a muscle? The insertion? The swell? What is the color of muscles? With what is each muscular fibre supplied? 154. What is said of fascia? What is its appearance when freshly exposed? 155. What effect has it on the muscles? Give other uses of the fascia. -=-=-=-=-=-=-=-=-=-=-=-= 156. The interstices between the different muscles are filled with adipose matter, or fat. This is sometimes called the packing of the system. To the presence of this tissue, youth are indebted for the roundness and beauty of their limbs. [Illustration: Fig. 37. A transverse section of the neck. The separate muscles, as they are arranged in layers, with their investing fasciæ, are beautifully represented. As the system is symmetrical, figures are placed only on one side. In the trunk the muscles are arranged in layers, surrounded by fasciæ, as in the neck. The same is true of the muscles of the upper and lower limbs. 12, The trachea, (windpipe.) 13, The oesophagus, (gullet.) 14, The carotid artery and jugular vein. 28, One of the bones of the spinal column. The figures that are placed in the white spaces represent some of the fasciæ; the other figures indicate muscles.]