434 MYOLOGY 



muscular fibers from the external lip of the crest of the ilium lateral to the margin 

 of the Sacrospinalis, and from the three or four lower ribs by fleshy digitations, 

 which are interposed between similar processes of the Obliquus abdominis externus 

 (Fig. 392, page 409). From this extensive origin the fibers pass in different direc- 

 tions, the upper ones horizontally, the middle obliquely upward, and the lower 

 vertically upward, so as to converge and form a thick fasciculus, which crosses the 

 inferior angle of the scapula, and usually receives a few fibers from it. The muscle 

 curves around the lower border of the Teres major, and is twisted upon itself, so 

 that the superior fibers become at first posterior and then inferior, and the vertical 

 fibers at first anterior and then superior. It ends in a quadrilateral tendon, about 

 7 cm. long, which passes in front of the tendon of the Teres major, and is inserted 

 into the bottom of the intertubercular groove of the humerus; its insertion extends 

 higher on the humerus than that of the tendon of the Pectoralis major. The lower 

 border of its tendon is united with that of the Teres major, the surfaces of the two 

 being separated near their insertions by a bursa; another bursa is sometimes inter- 

 posed between the muscle and the inferior angle of the scapula. The tendon of 

 the muscle gives off an expansion to the deep fascia of the arm. 



Variations. The number of dorsal vertebrae to which it is attached vary from four to seven or 

 eight; the number of costal attachments varies; muscle fibers may or may not reach the crest of 

 the ilium. \ 



A muscular slip, the axillary arch, varying from 7 to 10 cm. in length, and from 5 to 15 mm. 

 in breadth, occasionally springs from the upper edge of the Latissimus dorsi about the middle 

 of the posterior fold of the axilla, and crosses the axilla in front of the axillary vessels and nerves, 

 to join the under surface of the tendon of the Pectoralis major, the Coracobrachialis, or the fascia 

 over the Biceps brachii. This axillary arch crosses the axillary artery, just above the spot usually 

 selected for the application of a ligature, and may mislead the surgeon during the operation. It 

 is present in about 7 per cent, of subjects and may be easily recognized by the transverse direction 

 of its fibers. 



A fibrous slip usually passes from the lower border of the tendon of the Latissimus dorsi, near 

 its insertion, to the long head of the Triceps brachii. This is occasionally muscular, and is the 

 representative of the Dorsoepitrochlearis brachii of apes. 



The lateral margin of the Latissimus dorsi is separated below from the Obliquus 

 externus abdominis by a small triangular interval, the lumbar triangle of Petit 

 the base of which is formed by the iliac crest, and its floor by the Obliquus intermit 

 abdominis. Another triangle is situated behind the scapula. It is bounded above 

 by the Trapezius, below by the Latissimus dorsi, and laterally by the vertebral 

 border of the scapula; the floor is partly formed by the Rhomboideus major. 

 If the scapula be drawn forward by folding the arms across the chest, and the 

 trunk bent forward, parts of the sixth and seventh ribs and the interspace between 

 them become subcutaneous and available for auscultation. The space is there- 

 fore known as the triangle of auscultation. 



Nerves. The Trapezius is supplied by the accessory nerve, and by branches from the third 

 and fourth cervical nerves; the Latissimus dorsi by the sixth, seventh, and eighth cervical nerves 

 through the thoracodorsal (long subscapular) nerve. 



The Rhomboideus major (Fig. 409) arises by tendinous fibers from the spinous 

 processes of the second, third, fourth, and fifth thoracic vertebrae and the supra- 

 spinal ligament, and is inserted into a narrow tendinous arch, attached above to 

 the lower part of the triangular surface at the root of the spine of the scapula; 

 below ^o the inferior angle, the arch being connected to the vertebral border by a 

 thin membrane. When the arch extends, as it occasionally does, only a short 

 distance, the muscular fibers are inserted directly into the scapula. 



The Rhomboideus minor (Fig. 409) arises from the lower part of the ligamentum 

 nuchse and from the spinous processes of the seventh cervical and first thoracic 

 vertebrae. It is inserted into the base of the triangular smooth surface at the root 

 of the spine of the scapula, and is usually separated from the Rhomboideus major 





