GENERAL MORPHOLOGY OF THE MUSCLES. 201 



to other tendinous bands which intersect its substance ; and thus the muscular 

 fibres run into these tendinous parts with various degrees of obliquity to the axis of 

 the muscle. 



The muscular flesh forms a large proportion of the weight of the whole body. 

 The following has been calculated for a man of 150lb. weight from the tables of 

 G-. v. Liebig : l skeleton, 28 Ib. ; muscles, 62 Ib. ; viscera (with skin, fat, blood, &c.), 

 60 Ib. 



General morphology. It is obvious that the disposition of the muscles, as a whole and 

 in groups, originally bears a close relation to the plan of vertebrate organization in the 

 skeleton. This is very perceptible in the earlier stages of foetal development and in the lowest 

 vertebrate animals. In fishes especially, and partly in amphibia, the muscles present a 

 remarkable degree of vertebrate segmentation, the greater part of the muscles of the trunk 

 being subdivided into zones, myomeres or myotomes, by membranous partitions, myocommatu 

 or sclerotomes, which extend transversely through the walls of the trunk, and in which the 

 neural arches of the vertebras and the costal arches are developed. In the higher animals and 

 in man, together with the greater specialization of muscles in connection with the develop- 

 ment of limbs, great deviations from the primitive muscular type in the trunk have occurred, 

 and it becomes extremely difficult to trace the morphological relations of many of the muscles 

 in the axial part of the body. It is indeed only in the deeper muscles of the vertebral column 

 and of the ribs that the vertebrate subdivision and relation remain in any degree apparent. 

 In the more superficial muscles, and more especially in the muscles of the limbs, where the 

 direction of the fibres is generally outwards from the trunk, portions of the myomeres run 

 together so as to form muscles of greater or less length, in which all appearance of vertebrate 

 division is effaced. In their more general relations to the trunk of the body two sets of the 

 muscles may be distinguished as epaxial and hypaxial, according as they lie above or below 

 the embryonic vertebral axis and the plane of its lateral extension. The hypaxial or sub- 

 nrtebral muscles, comparatively little developed in man, comprise chiefly the prevertebral 

 muscles of the neck with a part of the diaphragm. Of the epaxial muscles a dorso-lateral 

 division consists mainly of the long and short extensor muscles of the spine and head ; while a 

 centra-lateral division consists both of such ventral longitudinal muscles as the genio-hyoid, 

 sterno-hyoid, and rectus abdominis, and of the lateral, obliquely directed, sterno-mastoid, 

 scalene, intercostal, and abdominal muscles. The muscles of the limbs are also primarily 

 derived from this great ventro-lateral muscle. They may be distinguished as extrinsic when 

 attached partly to the limbs and partly to the trunk, and as intrinsic when wholly attached 

 to the bones of the limbs and their arches. 



To these morphological relations farther reference will hereafter be made under the 

 several large divisions of the muscles. (See Humphry, " Observations in Myology," &c., 1872, 

 and in various papers in the Journ. of Anat. ; Huxley, " Anat. of Verteb. Animals ; " Mivart, 

 ' Lessons in Elementary Anatomy; " Wiedersheim, " Lehrb. d. vergl. Anat. d. Wirbelthiere.") 



Homologles and varieties. It follows from what has been stated above, that homo- 

 logous correspondence can be traced between the individual muscles and groups of muscles of 

 man and those of animals. But as the form and attachments of the muscles are subject to 

 very great variation in different animals, as well as to occasional varieties in the same species, 

 the determination of the special homologies is attended in many cases with great difficulty, 

 and is still very imperfect. Many varieties have also been observed in the human body, and 

 it is interesting to notice that these varieties are found to reappear generally in the same 

 form, or in modifications of it which indicate .relations to a typical or fundamental structure ; 

 and that many of them are thus more or less repetitions of forms known to exist in different 

 species of the lower animals. (Consult Wood in Proceedings of Roy. Soc., 1864-68 ; Macalister's 

 Catalogue of Muscular Anomalies, in Trans. Roy. Irish Acad., 1872 ; Wenzel Gruber, in Mem. 

 of the Petersburg Acad., Virchow's Archiv, and " Beobachtungen aus der menschlichen und 

 vergleichenden Anatomic"; Henle's "Handbuch," " Muskellehre," 2nd Ed., 1871; Krause, 

 " Handbuch," 3rd Ed., vol. iii, 1880; Testut, "Les anomalies musculaires chez I'homme 

 expliquees par 1'anatomie comparee," 1884.) 



1 Archiv f. Anat. u. Physiol., 1874. The weights of the several muscles in a number of subjects 

 of both sexes and at various ages are given by F. W. Theile, ' ' Grewichtsbestimmungen zur Entwickelung 

 des Muskelsystems und des Skelettes beim Menschen," Nova Acta d. k. Leop. -Carol. Akad. d. Naturf., 

 Band xlvi, Nr. 3, Halle, 1884. 



