THE MUSCLES AND FASCLE.' 



MYOLOGY is the branch of anatomy which treats of the muscles. The 

 muscles are formed of bundles of reddish fibres, endowed notably with the 

 property of contractility in the direction of the long axes of the muscle cells. 

 Contractions of muscle fibres induce motion. The two principal kinds of muscle 

 tissue found in the body are the more highly differentiated, or voluntary, and 

 the less highly differentiated, or involuntary. The former of these, from the char- 

 acteristic appearances which its fibres exhibit under the microscope, is known as 

 striated, or striped muscle. As most striped muscles are capable of being put into 

 action and controlled by the will, they are generally called "voluntary" muscles. 

 The fibres of involuntary muscle do not present any cross-striped appearance, and 

 are not under the control of the will; such muscles are known as unstriated, un- 

 striped or vegetative. The muscle fibres of the heart differ in certain particulars 

 from both these groups, and they are therefore separately described as cardiac 

 muscle fibres. 



Thus, it will be seen that there are three varieties of muscle tissue: (1) Trans- 

 versely striated fibres, which are for the most part voluntary and under the control 

 of the will. This variety of muscle is also called skeletal. (2) Transversely 

 striated muscle fibres, which are not under the control of the will i. e., the 

 cardiac muscles. The cardiac muscle occupies a mid-position in the scale be- 

 tween the cells of involuntary and the striated fibres of voluntary muscle. (3) 

 Plain or unstriped muscle fibres, which are involuntary, and are controlled by 

 a different part of the nerve system from that which controls the activity of the 

 voluntary muscles. Such are the muscular walls of the stomach and intestine, 

 of the uterus and bladder, of the bloodvessels, of certain canals and ducts, etc. 

 The statement that striated muscle is always voluntary, and that nonstriated 

 muscle is always involuntary, cannot be accepted as invariably and inevitably 

 true. There are animals in which some voluntary muscle is free from distinct 

 striation. 



Although the voluntary striated muscle tissue alone is concerned in the skeletal 

 musculature, all three varieties of muscle tissue will be described here. The 

 skeletal muscles act upon the bones, and thus produce movement. The primitive 

 contractile elements of a muscle are the fibres. Fibres are gathered into groups 

 known as primary bundles or fasciculi, and the fasciculi are aggregated into masses 

 called secondary bundles. In coarse muscles the fasciculi are of considerable 

 size; in fine muscles they are of trivial size. Fasciculi may be long or short, 

 and the length does not depend on the length of the muscle. 



Structure of Striated Muscle. Each muscle is surrounded by a sheath of fibrous tissue 

 called the epimysium; this sends in septa which surround the secondary bundles; these in 

 turn send in the perimysium which surrounds each muscle fasciculus. The fibres of each 

 fasciculus are separated by a delicate meshwork of fibroelastic tissue, the endomysium, which 

 supports the small vessels and nerves. 



1 The Muscles and Fasciae are described conjointly, in order that the student may consider the arrangement 

 of the latter in his dissection of the former. It is rare for the student of anatomy in this country to dissect 

 the fascia; separately; and it is for this reason, as well as from the close connection that exists between the 

 muscles and their investing sheaths, that they are considered together. Some general observations are first 

 made on the histology and anatomy of the muscles and fasciae, the special description being given in connection 

 with the different regions. 



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