NOMENCLATURE 319 



fibre there is distributed a terminal nerve-fibre which passes through the sarcolemma and ends 

 in a motor end organ (muscle plate). Occasionally there are two such nerve-fibres to one muscle- 

 fibre. 



Vessels. — The muscles are richly supplied with blood. In many instances the 

 larger blood-vessels accompany the larger nerve-trunks as they enter the muscle, 

 and their primary branches are distributed in the larger intramuscular septa. 

 Often, however, the main blood-vessels approach a muscle from a direction dif- 

 ferent from that taken by the nerves. Each muscle has, however, its own blood 

 suppty. There is little anastomosis between the blood-vessels of a muscle and 

 those of a neighbouring structure, but the anastomosis between the vessels within 

 the muscle is exceedingly rich. Veins, as a rule, accompany all but the smallest 

 arteries within the muscle. The veins are richly supplied with valves, so that 

 muscle contraction promotes the flow of blood through the muscle. Rich cap- 

 illary plexuses surround the muscle-fibres. The capillaries are of unusually 

 small diameter. 



During contraction, the blood is forced from the muscles; during expansion 

 it rushes in through dilated arteries which furnish five or six times as much 

 blood to muscles during exercise as that supplied to them during rest. 



The connective-tissue sheaths, the larger intramuscular septa, and the tendons 

 of muscles are richly supplied with lymphatics. There are no lymphatics within 

 the muscle bundles or in small muscles. 



Nomenclature. — The names of the various muscles and their classification are 

 less satisfactory than is desirable. The muscular system was first carefully 

 studied in the human body, and names based sometimes upon the shape, structm'e, 

 size, or position, at other times upon the supposed function or other associated 

 facts, were applied to the muscles found in various regions. Sometimes two or 

 more names were applied to a muscle to indicate sevei'al of these factors. Thus 

 trapezius and triangularis indicate the shape of the corresponding muscles; biceps 

 or triceps indicates the origin by two or three heads; rectus, ohliquus, and trans- 

 versus represent the direction taken by a muscle or its constituent fibre-bundles; 

 magnus and minimus indicate size; suhlimis (superficial) and profundus (deep) 

 represent the relative positions occupied; sterno-cleido-mastoid indicates structures 

 to which the muscle is attached; flexor and extensor indicate function; and sar- 

 torius indicates that the corresponding muscle was supposed to be of use to tailors. 



Since careful study has been devoted to the comparative anatomy of the muscles in 

 various vertebrates, it has become apparent that a simple and more consistent nomenclature 

 applicable to corresponding muscles found in various animals would be of gi-eat value. A 

 satisfactory nomenclature of this sort has not, however, as yet been devised and adopted in 

 comparative anatomy, and the established usage of the terms now familiarly applied to the 

 muscles of the human body makes it seem improbable that even if such a system were devised 

 for comparative anatomy it could be brought into extensive use in human anatomy. For 

 many of the muscles in the human body various synonyms have been in use in different countries. 

 The Anatomical Congress assembled at Basel in 1895, to simphfy the nomenclature of human 

 anatomy, adopted in large part the terms in familiar use in England and America. In the 

 following pages the terms approved by the Congress will be employed, but where they differ 

 materially from those previously in use, the synonym will be given in parentheses. 



Classification. — The muscles are usually treated strictly according to the region of the body 

 in which they are found. This method of consideration is still of value in a dissector's guide and 

 in text-books of topographical anatomy. But in studying the muscles scientifically it is of 

 importance also to consider them in their more fundamental genetic relationships to one another 

 and to the nervous system. Embryology and comparative anatomy have proved of the gi-eatest 

 value in reveahng these relationships. Studies of this nature have revealed well-marked rela- 

 tionships in tjne adult human musculature which are of practical as well as scientific importance 

 The voluntary musculature may be broadly divided into that of the skeletal axis, the limbs, and 

 the visceral orifices. The musculature of each of these divisions has a different and in general 

 simpler form in the lower than in the higher vertebrates, and in the embryos of thp higher 

 vertebrates than in the adult. The musculature of the spinal region of the body axis of fishes, 

 the tailed amphibia, and all vertebrate embryos is metamerically segmented; that is, it is divided 

 along the axis of the body into a series of components corresponding with the segmentation of 

 the vertebral column. Although marked alterations take place in the subsequent ontogenetic 

 differentiation in higher vertebrates, traces of this primitive segmentation are still to be found 

 in the adult; in man, for instance, in the intercostal muscles and the segments of the rectus ab- 

 dominis. In the region of the head conditions are complex, owing to the concurrent presence 

 of muscles which primitively correspond in nature with the segmental spinal musculature, and 

 muscles non-segmental in character, which surround the visceral orfices. This also is true of 

 the anus and external genitalia, where, however, the conditions are simpler. Embryology and 

 comparative anatomy have done much to clear up puzzling features in both regions. 



The muscles of the hmbs are metamerically arranged in no adult vertebrate. In some of the 

 lower forms a series of axial muscle segments, myotomes, furnishes material from which the 



