468 HUMAN ANATOMY, 



the segmental nerve, or at least those fibres of it which originally supplied the por- 

 tions of the myomeres in question, retains its connection and is consequently drawn 

 out far beyond its usual territory, a ready explanation being thus afforded for the 

 extended course of the long thoracic, long subscapular, and phrenic ner\'es. The 

 muscles supplied by these nerves, as well as the pectoralis major and minor muscles, 

 are all derived from cervical myomeres, their adult position being due to the process 

 of migration, of whose existence they form convincing examples. 



6. Finally, portions of one or several successive myomeres may undergo degen- 

 eration, becoming converted into connective tissue, which may have the form of 

 fascia, aponeurosis, or tendon. Examples of this degeneration are to be found in 

 practically all muscles, since the tendons by which they make their bony attachments 

 have resulted from its action. In the lower vertebrates and in the foetus tendons 

 and aponeuroses are much less developed than in the higher forms or in the adult, 

 being represented by muscular tissue which later becomes converted into tendon or 

 aponeurosis. The intermuscular septa between the muscles of the limbs seem to 

 have arisen in this way, and occasionally relatively large aponeurotic sheets have so 

 arisen, as in the case of the aponeurosis which unites the two posterior serratus 

 muscles. . Of especial interest in this connection are the degenerations into liga- 

 ments of muscle-tissue primarily occurring in the neighborhood of many of the 

 joints, the accessory ligaments being in many cases formed in this manner. Thus, 

 the external lateral ligament of the knee-joint, the ligamentum teres of the hip-joint, 

 and even the great sacro-sciatic ligament owe their origin to this process, and many 

 other of the ligaments may also be referred to it. 



As a result of these various modifications and their combinations the indi\idual 

 muscles of the adult body, together with the aponeurotic sheets which are frequently 

 associated with them, are formed. 



GENERAL CONSIDERATION OF THE VOLUNTARY MUSCLES. 



The voluntary or striated muscles constitute a very considerable portion of the 

 entire mass of the body, their weight in an average adult male having been esti- 

 mated at about 43.4 per cent, of the total body weight (Vierordt). Each muscle 

 is a distinct organ composed of a number of contractile fibres united into bundles or 

 fasciculi surrounded by a delicate sheath of connective tissue, the perimysitim, in 

 which blood-vessels and nerves ramify to the various fasciculi, and which, at the 

 surface of the muscle, is continuous with the fascia which encloses the entire organ. 



At each extremity of the niuscle the contractile tissue is united with dense 

 connective tissue, the general structure of which resembles that of the muscle, its 

 fibres being arranged in distinct bundles separated and enclosed by looser tissue 

 comparable to the perimysium. By means of these te7ido7is, as they may generi- 

 cally be termed, the attachment of the muscle to portions of the skeleton or other 

 structures is effected. The extent to which the tendon is developed varies greatly 

 in different muscles, in some being hardly noticeable, so that the muscle-tissue 

 appears to be directly attached to the bone (Fig. 496), at other times forming a 

 long rounded or flattened band (Fig. 576), to which the term tendon is usually 

 applied, or again forming a broad, flat expansion, termed an aponetirosis (Fig. 525), 

 Both the tendons and aponeuroses are to be regarded as representing portions of the 

 original muscle converted into connective tissue, and, indeed, comparative anatomy 

 shows that many of the ligaments and aponeuroses of the body, even although they 

 may not seem to be directly related to neighboring muscles, are really to be regarded 

 as muscles which have undergone a tendinous degeneration. 



Attachments. — The great majority of the voluntary muscles are attached at 

 either end to portions of the skeleton, passing over oite or more joints, in which 

 they effect movement by their contraction. Occasionally, however, a muscle may 

 be attached at one of its extremities, in part or entirely, to fascia, as, for instance, 

 the gluteus maximus and the tensor fascice latse, or both of its attachments may be 

 to fascia, as is the case with some of the muscles of expression and with the muscles 

 of the palate and the intrinsic musculature of the tongue. Others, again, may have 

 their attachments to tendons of other muscles, — e.g., the flexor accessorius pedis 



