THE MUSCULAR TISSUE. 1107 



an account of these the reader must be referred to the description of the individual 

 bones in the sequel. 



A knowledge of the exact periods when the epiphyses become joined to the 

 shaft is often of great importance in medico-legal inquiries. It also aids the sur- 

 geon in the diagnosis of many of the injuries to which the joints are liable; for it 

 not infrequently happens that, on the application of severe force to a joint, the 

 epiphysis becomes separated from the shaft, and such injuries may be mistaken for 

 fracture or dislocation. 



THE MUSCULAR TISSUE. 



The muscles are formed of bundles of reddish fibres, endowed with the property 

 of contractility. The two principal kinds of muscular tissue found in the 

 body are voluntary and involuntary. The former of these, from the character- 

 istic appearances which their fibres exhibit under the microscope, are known as 

 the "striped" muscles, and from the fact that it is capable of being put into 

 action and controlled by the will, as "voluntary" muscle. The fibres of the 

 latter do not present any cross-striped appearance, and for the most part are 

 not under the control of the will; hence they are known as the "unstriped" or 

 "involuntary" muscles. The muscular fibres of the heart differ in certain par- 

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

 " cardiac " muscular fibres. 



Thus it will be seen that there are three varieties of muscular fibres : (1) 

 Transversely striated muscular fibres, which are for the most part voluntary and 

 under the control of the will, but some of which are 

 not so, such as the muscles of the pharynx and upper 

 part of the oesophagus. This variety of muscle is 

 sometimes called skeletal. (2) Transversely striated 

 muscular fibres, which are not under the control of 

 the will i. e., the cardiac muscle. (3) Plain or un- 

 striped muscular fibres, which are involuntary and 

 controlled by a different part of the nervous 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 blood- 

 vessels, etc. 



The striped or voluntary muscles are composed of 

 bundles of fibres enclosed in a delicate web called the FIG. 637. Transverse section from 



. ,, . j- , ,1 ~'U_,iV. * the stfrno-mastoid in man. Magni- 



" penmysmm, in contradistinction to trie sneatn 01 fled 50 times, o. External perimys- 

 areolar tissue which invests the entire muscle, the griiny^^fe. c- 

 "epimysium" (Fig. 637). The bundles are termed 



"fasciculi"; they are prismatic in shape, of different sizes in different muscles, 

 and for the most part placed parallel to one another, though they have a tendency 

 to converge toward their tendinous attachments. Each fasciculus is made up of 

 a bundle of fibres, which also run parallel with each other, and which are sepa- 

 rated from one another by a delicate connective tissue derived from the perimys- 

 ium, and termed endomysium. This does not form the sheath of the fibres, but 

 serves to support the blood-vessels and nerves ramifying between them. The 

 fibres are enclosed in a separate and distinct sheath of their own, but it is not 

 areolar tissue, and is therefore not derived from the perimysium. 



A muscular fibre may be said to consist of a soft contractile substance en- 

 closed in a tubular sheath, named by Bowman the sarcohmma. The fibres are 

 cylindrical or prismatic in shape, and are of no great length, not exceeding, it is 

 , said, an inch and a half. They end either by blending with the tendon or 

 aponeurosis, or else by rounded or tapering extremities which are connected to the 

 neighboring fibres by means of the sarcolemma. Their breadth vanes m man 

 from a,,- to ^ of an inch. As a rule, the fibres do not divide or anastomose; 

 but occasionally, especially in the tongue and facial muscles, the fibres may b 



