STRUCTURE OF MUSCLE. 169 



longitudinal, and terminate at each extremity in tendon, the entire muscle 

 being fusiform in its shape ; in other situations they are disposed like the 

 rays of a fan, converging to a tendinous point, as the temporal, pectoral, 

 glutei, &c., and constitute a radiate muscle. Again, they are penniform, 

 converging like the plumes of a pen to one side of a tendon, which runs 

 the whole length of the muscle as in the peronei ; or bipennifortn, con- 

 verging to both sides of the tendon. In other muscles the fibres pass 

 obliquely from the surface of a tendinous expansion spread out on one 

 side, to that of another extended on the opposite side, as in the semi- 

 membranosus ; or, they are composed of penniform or bipenniform fasci- 

 culi as in the deltoid, and constitute a compound muscle. 



The nomenclature of the muscles is defective and confused, and is 

 generally derived from some prominent character which each muscle pre- 

 sents ; thus, some are named from their situation, as the tibialis, peroneus; 

 others from their uses, as the flexors, extensors, adductors, abductors, le- 

 vators, tensors, &c. Some again from their form, as the trapezius, trian- 

 gularis, deltoid, &c. ; and others from their direction, as the rectus, 

 obliquus, transversalis, &c. Certain muscles have received names ex- 

 pressive of their attachments, as the sterno-mastoid, sterno-hyoid, &c. ; and 

 others, of their divisions, as the biceps, triceps, digastricus, complexus, &c. 



In the description of a muscle we express its attachment by the words 

 " origin" and " insertion ;" the term origin is generally applied to the 

 more fixed or central attachment, or to the point towards which the motion 

 is directed, while insertion is assigned to the more movable point, or to 

 that most distant from the centre ; but there are many exceptions to this 

 principle, and as many muscles pull equally by both extremities, the use 

 of such terms must be regarded as purely arbitrary. 



In structure, muscle is composed of bundles of fibres of variable size 

 called fasciculi, which are enclosed in a cellular membranous investment 

 or sheath, and the latter is continuous with the cellular framew r ork of the 

 fibres. Each fasciculus is composed of a number of smaller bundles, and 

 these of single fibres, which, fron* their minute size and independent ap- 

 pearance, have been distinguished by the name of ultimate fibres. The 

 ultimate fibre is found by microscopic investigation to be itself a fasciculus 

 (ultimate fasciculus), made up of a number of ultimate fibrils enclosed in 

 a delicate sheath or myolemma.* Two kinds of ultimate muscular fibre 

 exist in the animal economy ; viz., that of voluntary or animal life, and 

 that of involuntary or organic life. 



The ultimate fibre of animal life is known by its size, by its uniformity 

 of calibre, and especially by the very beautiful transverse markings which 

 occur at short and regular distances throughout its whole extent. It also 

 presents other markings or striaB, having a longitudinal direction, which 

 indicate the existence of fibrillae within its myolemma. The myolemma, 

 or investing sheath of the ultimate fibre, is thin, structureless and trans- 

 parent. 



* In the summer of 1836, while engaged with Dr. Jones Quain in the examination of 

 the animal tissues with a simple dissecting microscope, constructed by Powell, I first 

 saw that the ultimate fibre of muscle was invested by a proper sheath, for which I pro- 

 posed the term "Myolemma;" a term which was adopted by Dr. Quain in the fourth 

 edition of his " Elements of Anatomy." We at that time believed that the transverse 

 folding of that sheath gave rise to the appearance of transverse striae, an opinion whic> 

 subsequent examinations proved to be incorrect. Mr. Bowman employs the term " Sar- 

 colemma," as synonymous with Myolemma. 



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