J 4 6 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



between it and the splenius capitis. The deltoid has its origin immediately adjacent to the 

 insertion of the trapezius, and a small transverse muscle occasionally passes between the insertions 

 of the trapezius and the sternocleidomastoid; it is known as the transversa nucha (Fig. 244)^ 

 and usually has a tendinous origin from the tendon of one muscle and passes to the tendon of the 

 other. 



The trapezius is supplied by the accessory nerve and by the cervical plexus. 



On account of the different directions taken by the fibers in different portions of the trapezius the function of 

 the muscle is comphcated, and differs according to whether all portions of the muscle contract simultaneously or individ- 

 ual portions contract separately. Its action also depends upon whether the scapula is fixed or movable The upper 

 portion of the trapezius elevates the entire shoulder girdle, the lower portion pulls the scapula downward and the middle 

 portion draws the scapula backward toward the vertebral column. The scapula is also drawn backward by the action 

 of the entire muscle, since the upper and lower fasciculi neutralize each other to a certain extent and aid" the middle 

 portion of the muscle. If the shoulder-blade is fixed, the muscle turns the head; when both scapula: are fixed and 

 the two muscles act together, the head is extended. The muscle may also fix the scapula. It usually acts together with 

 the levator scapuh, the rhomboidei, the splenii, and the other muscles of the back. 



The latissimus dorsi (Figs. 236, 238, 269, and 272) is a broad, thin, triangular muscle which 

 becomes somewhat thicker toward its insertion. The upper portion of its origin is partly con- 

 cealed by the trapezius, and it is situated in the median dorsal, the sacral, the lumbar, the' infra- 

 scapular, and the scapular regions. Its origin is tendinous throughout, with the exception of 

 three or four accessory digitations which arise from the three or four lower ribs. The tendon of 

 origin is furnished by the posterior surface of the posterior layer of the lumbodorsal fascia (see 

 page 156), by means of which the muscle arises from the spinous processes of the lower five or 

 six thoracic vertebrae, from the spinous processes of the lumbar vertebrae, and from the median 

 ridge of the sacrum and the neighboring portion of the outer lip of the crest of the ilium. The 

 superior fibers run almost horizontally; the inferior fibers ascend abruptly from within outward 

 and from below upward, and toward the insertion the fibers converge, and terminate in a flat 

 tendon which is adherent to that of the teres major and is inserted with it into the lesser tubercular 

 ridge (the posterior lip of the bicipital groove) of the humerus. An almost constant bursa the 

 latissimus bursa, separates the non-adherent portions of the tendons of the latissimus dorsi'and 

 teres major. 



The tendinous surface of the posterior layer of the lumbodorsal fascia (Figs. o 3 g and 24o) 

 is widest in the region of the middle and lower lumbar vertebra?, and it becomes markedly nar- 

 rower as it extends upward, and to a lesser degree as it passes downward. Between the upper 

 border of the latissimus, the lower border of the trapezius, and the vertebral border of the scapula 

 there is a triangular space, which is larger or smaller according to the position of the scapula and 

 in which arc visible a portion of the rhomboideus major, small portions of one or more of the 

 middle ribs with their intercostal muscles, and a segment of the iliocostalis dorsi Upon the 

 neighboring dorsal surface of the scapula, the dense infraspinatus fascia covers the infraspinatus 

 muscle, and a portion of the deltoid muscle, covered by its fascia, is also visible in this situation 



The costal serrations of the latissimus dorsi interdigitatc with the inferior serrations of the 

 obhquus abdominis externus (Fig. 247). Between the outer border of the latissimus the pos- 

 terior border of the external oblique, and the crest of the ilium there is usually a small triangle 





