STRUCTURE OF MUSCLE. 



141 



muscle presents : thus, some are named from their situation, as the 

 tibialis, peroneus ; others from their uses, as the flexors, extensors, 

 adductors, abductors, levators, tensors, &c. Some again from their 

 form, as the trapezius, triangularis, deltoid, &c.; and others from 

 their direction, as the rectus, obliquus, transversalis, &c. Some 

 muscles have received names expressive 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 Fig. 66.* 



thewords "origin" and "inser- 

 tion;" the term origin being gene- 

 rally applied to the more fixed 

 or central attachment, or to the 

 point towards which the motion 

 is directed, while insertion is as- 

 signed to the more movable point, 

 or to that, most distant from the 

 centre; but there are many ex- 

 ceptions 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 

 framework of the fibres. Each fasciculus is composed of a number 

 of smaller bundles, and these of single fibres, which, from their minute 

 size and independent appearance, have been distinguished by the 

 name of ultimate fibres. The ultimate fibre is found by microsco- 

 pic investigation, to be itself made up of a number of ultimate fibrils 

 enclosed in a delicate sheath or myolemma.f Two kinds of ulti- 

 mate muscular fibre exist in the animal economy ; viz., that of 

 voluntary or animal life, and that of involuntary or organic life. 



* A. A muscular fibre of animal life enclosed in its myolemma ; the transverse and 

 longitudinal striae are seen. 



B. An ultimate fibril of muscular fibre of animal life. 



c. A muscular fibre of animal life, similar to A but more highly magnified.. Its 

 myolemma is so thin and transparent as to permit the ultimate fibrils to be seen through. 

 The true nature of the longitudinal striae is seen in this fibre as well as the mode of for- 

 mation of the transverse striae. 



D. A muscular fibre of organic life from the urinary bladder, magnified 600 times, 

 linear measure. Two of the nuclei are seen. 



E. A muscular fibre of organic life, from the stomach, magnified 600 times. The 

 diameter of this and of the preceding fibre, midway between the nuclei, was 1 -4750th 

 of an inch. 



t 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 proposed 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 trans- 

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

 which subsequent examinations proved to be incorrect. Mr. Bowman employs the 

 term " Sarcolemma" as synonymous with Myolemma. 



