470 HUMAN ANATOMY. 



alternate with one another, the muscle having thus a compound pinnate arrangement 

 (Fig. 491, C ). 



As a rule, the tendons occur in connection with the extremities of the muscle, 

 but occasionally one or more tendinous intersections may occur in the course of the 

 muscle, which thus becomes divided into two or more bellies. This condition may 

 be the result of the end-to-end union of the tendons of attachment of two primarily 

 distinct muscles {^e.g., digastric. Fig. 497) or to the persistence of some of the 

 dividing lines which separate the various embryonic segments of which a muscle 

 may be composed {^e.g., rectus abdominis, Fig. 523) ; or it may be due to a sec- 

 ondary attachment formed by a muscle in its course, it being bound down to a 

 neighboring bone by a band of fascia {e.g., omo-hyoid). 



Certain muscles present the peculiarity of possessing two or more separate 

 heads of origin, attached to different bones and uniting to form a common tendon of 

 insertion. In certain cases {e.g., biceps femoris, pronator radii teres) this condition 

 indicates the union of two primarily distinct muscles which had a common insertion, 

 or which were, at all events, originally inserted close together, but in other cases it 

 has resulted from a separation of an original muscle into two portions. The ana- 

 tomical nomenclature is not quite consistent as regards such muscles, since it 

 describes the biceps femoris as a two-headed muscle, although its two heads are 

 fundamentally distinct organs ; while, on the other hand, it usually regards the 

 psoas and iliacus and the gastrocnemius and soleus as distinct muscles, notwith- 

 standing their common insertion. 



Fasciae. — -Connecting the various muscles and uniting them into groups, and 

 also surrounding the entire musculature of the body and separating it from the 

 deeper layers of the integument, are sheets of connective tissue known as fascice. 

 These sheets are by no means isolated portions of connective tissue, but are rather 

 to be regarded as parts of the general interstitial connective-tissue net-work which 

 traverses all parts of the body, thickened to form more or less definite sheets stand- 

  ing in relation to the neighboring organs. The density of the sheets varies greatly ; 

 in some regions they are imperfectly developed and may contain considerable 

 amounts of fat, while in others they form dense, glistening sheets resembling the 

 expansions of tendons mentioned above, and termed, like these, aponeuj-oses. 



It is convenient to recognize two principal layers of fasciae, the superficial and 

 the deep. 



The superficial fascia immediately underlies the skin of the entire body, and is 

 sometimes considered a portion of it and termed the panyiicuhis adiposus, since, 

 except in the eyelids, penis, scrotum, and labia minora, it contains considerable quan- 

 tities of fat. It is connected with the subjacent deep fascia by a more or less exten- 

 sively developed layer of areolar tissue, which, however, is lacking in certain regions, 

 such, for instance, as the face, the palmar surface of the hand, and the plantar 

 surface of the foot, where the superficial and deep fasciae are intimately united. 



The deep fascia, on the other hand, immediately covers and invests the muscles, 

 and in the intervals between them becomes continuous with the periosteal connec- 

 tive tissue enclosing the bones. Those lamellae of the fascia which dip down 

 between the muscles of the limbs — the intermuscidar septa — are frequently of con- 

 siderable firmness and serve for the origin of fibres of the neighboring muscles, and 

 occasionally muscles {e.g., soleus, levator ani) take their origin in part directly 

 from portions of the deep fascia, which then becomes thickened along the line of 

 the origin to form strong bands, termed arcus tendinei, attached at either extremity 

 to neighboring bones. 



Certain portions of the deep fascia, and especially of the intermuscular septa, 

 represent portions of the muscular system which have undergone tendinous degen- 

 eration, and are represented by muscular tissue in the lower vertebrates. Indeed, 

 the relative amount of aponeurotic and tendinous tissue, as compared with the mus- 

 cular, is very much greater in the higher than in the lower forms, and is appre- 

 ciably greater in the human embryo than in the adult, indicating a transformation 

 of one tissue into the other during the life of the individual. 



Tendon-Sheaths. — Where tendons run in grooves of bones, bands of dense 

 connective tissue extend across between the lips of the grooves, being continuous 



