GENERAL PHYSIOLOGY OF MUSCULAR TISSUE. 43 



such a manner that, by an alteration in their form, they can change not only 

 the position of the bones with reference to one another, but can also change 

 the individual's relation to surrounding objects. They are, therefore, the 

 active organs of both motion and locomotion, in contradistinction to the 

 bones and joints, which are but passive agents in the performance of the 

 corresponding movements. In addition to the muscle masses which are 

 attached to the skeleton, there are also other collections of muscle tissue sur- 

 rounding cavities such as the stomach, intestine, blood-vessels, etc., which 

 impart to their walls motility, and so influence the passage of a material 

 through them. 



Muscles produce movement of the structures to which they are attached 

 by the property with which they are endowed of changing their shape, short- 

 ening or contracting under the influence of a stimulus transmitted to them 

 from the nervous system. Muscles are therefore divided into: 



1. Voluntary muscles, comprising those whose activity is called forth by 

 stimuli of the nerves as the result of an act or effort of volition. 



2. Involuntary muscles, comprising those whose activity is entirely inde- 

 pendent of the volition. 



The voluntary muscles are also known from their attachment to the 

 skeleton as skeletal, and from their microscopic appearance as striped muscles. . 

 The involuntary muscles, from their relation to the viscera of the body, are 

 known also as visceral, and from their microscopic appearance as plain or 

 smooth muscles. 



General Structure of Muscles. All skeletal muscles consist of a central 

 fleshy portion, the body or belly, which is provided at either extremity with 

 a tendon in the form of a cord or membrane by which it is attached to the 

 bones. The body is the contractile region, the source of activity; the tendon 

 is a passive region, and merejy transmits the activity to the bones. 



A skeletal muscle is a complex organ consisting of muscular fibers, con- 

 nective tissue, blood-vessels, and lymphatics. The general body of the 

 muscle is surrounded by a dense layer of connective tissue, the epimysium, 

 which blends with and partly forms the tendon; from its inner surface septa 

 of connective tissue pass inward and group the muscle-fibers into larger and 

 smaller bundles, termed fasciculi. The fasciculi, invested by this special 

 sheath, the perimysium, are irregular in shape, and vary considerably in 

 size. The fibers of the fasciculi are separated from one another and sup- 

 ported by a delicate connective tissue, the endomysium. The connective 

 tissue thus surrounding and penetrating the muscle binds its fibers into a 

 distinct organ, and affords support to blood-vessels, nerves, and lymphatics. 

 The muscle fibers are arranged parallel to one another, and their direction 



