160 STRUCTURE OF MUSCLE. 



the tendon. In other muscles the fibres pass obliquely from the 

 surface of a tendinous expansion spread out on one side, to that of an- 

 other extended on the opposite side, as in the semi-membranosus ; or, 

 they are composed of penniform or bipenniform fasciculi as in the del- 

 toid, 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 

 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. Certain muscles have re- 

 ceived 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 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 invest- 

 ment or sheath, and the latter is continuous with the cellular frame- 

 work of the fibres. Each fasciculus is composed of a number of smaller 

 bundles, and these of singles fibres, which, from their minute size and 

 independent appearance, have been distinguished by the name of ulti- 

 mate 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 uni- 

 formity 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 striae, having a 

 longitudinal direction, which indicate the existence of fibrillfe within 



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

 nation 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 transverse folding of that sheath gave rise to 

 the appearance of transverse strife, an opinion which subsequent examinations 

 proved to be incorrect. Mr. Bowman employs the term " Sarcolemma," as 

 synonymous with Myolemma. 



