366 THE MUSCULAE SYSTEM. 



triangular flat tendon, beneath which a bursa is placed into a rough tuberosity 

 at the base of the spine of the scapula (Fig. 328, p. 367). The fibres inserted 

 into the clavicle, acromion, and the upper border of the spine of the scapula spread 

 over the adjacent subcutaneous surfaces of those bones for a variable distance. 

 The occipital portion of the muscle may be in the form of a separate slip, or may 

 be entirely absent. 



The trapezius is superficial in its whole extent. Its upper lateral border forms 

 the posterior limit of the posterior triangle of the neck. The inferior lateral border, 

 passes over the upper edge of the latissimus dorsi and the vertebral margin of the 

 scapula, and forms a boundary of the so-called triangle of auscultation, which is 

 completed, below, by the latissimus dorsi, and, laterally, by the vertebral margin of the 

 scapula. This space is partly filled up by the rhomboideus major. The muscle 

 overlaps the latissimus dorsi, and covers the levator scapulae, rhomboidei, and the 

 deeper axial muscles of the back, along with the ascending and the descending 

 branch of the transverse artery of the neck, the accessory nerve, and muscular 

 branches from the cervical plexus. 



Nerve-Supply. The trapezius has a double nerve-supply : (1) from the terminal fibres of 

 the accessory nerve, and (2) from the cervical plexus (C. 3. and 4.). The cervical nerves communi- 

 cate with the accessory nerve in the posterior triangle of the neck and beneath the trapezius. 



Action. The main action of the trapezius is to draw the scapula backwards and upwards. 

 The upper fibres of the muscle elevate the shoulder-girdle, while the lower fibres, pulling on the 

 base of the spine of the scapula, depress the vertebral margin ; the two movements result in a 

 rotation of the scapula, by which the glenoid cavity is tilted upwards, as in the movement of 

 raising the arm above the head in a forward direction. 



M, Latissimus Dorsi. The latissimus dorsi is a large triangular muscle 

 occupying the lower part of the back. It has a triple origin. The greater part 



Pectoralis major (origin) 



Sterno-cleido-mastoid 

 (clavicular origin) 



Sterno-hyoid (origin) 



Trapexius (insertiou)- 

 FIQ. 327. MUSCLE- ATTACHMENTS TO THE RIGHT CLAVICLE (Upper Surface). 



of the muscle arises (1) from the posterior layer of the lumbo-dorsal fascia. This 

 is a thick membrane which conceals the sacrospinalis muscle in the lower part oi 

 the back. Through it the latissimus dorsi gains attachment to the spines of thf 

 lower six thoracic vertebrse, the spines of the lumbar vertebrae, and the tendon 

 the sacrospinalis, with which the fascia blends below. It also arises laterally 

 from the posterior part of the lateral lip of the iliac crest. 



From its origin the muscle is directed upwards and laterally, its fibi 

 converging to the inferior angle of the scapula. In relation to its lateral am 

 upper borders additional fibres arise. (2) Along the lateral border muscular sli] 

 arise from the lower three or four ribs, interdigitating with the slips of 

 of the obliquus abdominis externus. (3) As the superior "border of tKe musck 

 passes, horizontally, over the inferior angle of the scapula, an additional flesh] 

 slip usually takes origin from that part of the bone and joins the muscle on its dee] 

 surface (Fig. 329, p. 368). 



Beyond the inferior angle of the scapula the latissimus dorsi, greatly narrowed 

 curves spirally round the teres major muscle, and forms the prominence of th( 

 posterior axillary fold. It ends in a ribbon-like tendon, which is closely adherent 

 at first, to the teres major, and is inserted into the floor of the intertubercular sulci 

 of the humerus, extending for about three inches distal to the distal and later* 

 part of the lesser tubercle (Fig. 336, p. 376). It is placed behind the axilla] 

 vessels and nerves, and in front of the insertion of the teres major, from whk 

 it is separated by a bursa. 



