THE MUSCLES AND FASCIA. 67 



THE MUSCLES AND FASCIAE. 



What are the Muscles? They are the active organs of locomotion, formed 

 of bundles of reddish fibres endowed with the property of shortening themselves 

 upon irritation, which is called muscular contractility, and chemically consisting 

 of syntonin, or muscular fibrin. 



How are the Muscles divided ? Into 2 great classes, (i) Voluntary, Striped, 

 or Muscles of animal life, comprise those which are under the control of the 

 will. (2) Involuntary t Unstriped, or Muscles of organic life, are those which 

 are not under the control of the will. 



Voluntary Muscular Fibre consists of fasciculi about ^ inch in diameter, 

 each surrounded by a tubular membranous sheath, the perimysium; and marked 

 by fine striae passing around them in curved parallel lines about TT 7 o inc ^ 

 apart. These fasciculi are formed of fibrillcz, each about T ^Q^ inch thick, 

 also striated, presenting the appearance of a row of minute particles, the 

 "sarcous elements" of Bowman, and surrounded by cellular tissue, the sarco- 

 lemma. 



Involuntary Muscular Fibre consists of flattened fusiform or spindle-shaped 

 fibres, averaging about ^V^ inch in breadth, consisting of elongated cells, and 

 bound together in bundles by areolar tissue. These fibres are found in the 

 alimentary canal, in the posterior wall of the trachea, in the bronchi, the ducts 

 of certain glands, in the ureters, bladder, urethra, genitalia of both sexes, walls 

 of all arteries and most veins and lymphatics, in the iris and ciliary muscle, 

 and in the skin. 



What are Tendons and Aponeuroses ? Tendons are white, glistening cords 

 or bands formed of white fibrous tissue almost entirely, have few vessels and 

 no nerves, and serve to connect the muscles with the structures on which they 

 act. Aponeuroses are fibrous membranes, of similar structure and appearance, 

 and serve the same purpose. 



What are Fasciae ? They are laminae of variable thickness which invest 

 (fascia, a bandage) the softer structures. The superficial fascia is composed 

 of fibro-areolar tissue, and is found beneath the skin almost over the whole 

 body. The deep fascia is of aponeurotic structure, dense, inelastic, and fibrous, 

 ensheathing the muscles and affording some of them attachment, also the vessels 

 and nerves, and binding down the whole into a shapely mass. 



To what Structures are Muscles attached? To the periosteum and peri- 

 chondrium of bone and cartilage, to the subcutaneous areolar tissue, and to 

 ligaments. In the latter case only are their tendons in direct contact with the 

 tissue on which they are to act. 



How many Muscles are Double-bellied ? Five, the occipito-frontalis, 

 biventer cervicis, digastric, omo-hyoid, and the diaphragm. 



