306 HEALTH AND DISEASE 



Non-Striated muscle is of a pale grayish hue, and enters into the 

 structure of hollow organs, such as the stomach and bowels, the uterus and 

 bladder, the blood-vessels, the bronchial tubes, &c. &c. It consists of a 

 number of minute spindle-shaped fibre-cells, about 45^ to ^-jo of an 

 inch in breadth and ^^ to 3-5-5 of an inch in length. Non-striated muscle 

 is not under the control of the will, its movements are therefore involuntary, 

 and carried on by reflex action. 



Voluntary muscles are distinguished from one another by various names. 

 Of these some refer to their action. Those which bend a joint, for instance, 

 are termed flexors, while others which straighten it again are known as 

 extensors. There are also levators, depressors, abductors, adductors, con- 

 strictors, dilators, &c. &c. 



Others are distinguished by their length, as the long muscle of the back, 

 longissimus dorsi, the short muscle of the tongue, hyo-glossus brevis. Size, 

 form, position, direction, and other qualities are also invoked as a means of 

 recognition. 



Voluntary muscles, with few exceptions, exist in pairs one on either 

 side of the body or organ in whose function they are engaged. They are 

 attached by their extremities to two or more bones, which they cause to 

 move at the instigation of the will. 



When in action one extremity of the muscle is fixed, the other is 

 movable. The former is termed its origin, or the part_/rom which it acts; 

 the latter is its insertion, or the part upon which it acts and moves. In 

 some instances the extremities are alternately fixed and movable; what is 

 at one time the origin is at another the insertion. This is the case with 

 the mastoido-humeralis, a long muscle running from the arm to the back of 

 the head. If when the arm is fixed the muscle contracts, the head is drawn 

 downwards and to one side; and conversely when the head is fixed, the 

 arm is raised. 



Tendons. Muscles are attached to bones either directly by their fleshy 

 fibres or by tendons which proceed from them. Tendons transmit the 

 action of muscles to the bones to be acted upon. They exist in the form 

 of dense rounded cords of various lengths, or as more or less broad, flat, 

 expanded sheets. In the latter condition they are spoken of as aponeurotic 

 tendons, and are found in their highest development in connection with the 

 muscles of the belly, where they assist in forming the abdominal walls. 

 The long cord-like variety are met with in the extremities, where the more 

 important extend from above the knees and hocks downward to the feet 

 and pasterns. 



Some tendons are partly or completely surrounded by a fibrous sheath, 

 and this is lined by a synovial membrane, which, being also reflected on to 



