THE UPPER LIMB ' 287 



posterior border of the obliquus externus abdominis. If it does not 

 do so, a small space is left, called the triangle of Petit, which is situ- 

 ated immediately above the centre of the iliac crest. It is bounded 

 in front by the posterior border of the obliquus externus abdominis, 

 behind by the anterior border of the latissimus dorsi, and below by 

 the iliac crest near the centre. It is covered only by skin and 

 fascia, and its floor is formed by a part of the obliquus intemus 

 abdominis. In this situation a lumbar hernia may occur, or a 

 lumbar abscess may find its way to the surface. 



Levator Anguli Scapulae — Origin. — By four tendinous slips from 

 the posterior tubercles of the transverse processes of the first four 

 cervical vertebrae. 



Insertion. — The base of the scapula from the superior angle to the 

 triangular surface at the root of the spine. 



Nerve-supply. — Branches of the cerv^ical plexus, which are derived 

 from the third and fourth cervical nerves, and a branch from the 

 nerve to the rhomboids. 



The muscle is directed downwards, back\vards, and slightly 

 outwards. 



Action. — Acting from its origin the muscle elevates the superior 

 angle of the scapida, thereby rotating the bone and causing the point 

 of the shoulder to be depressed. Acting from its insertion it is a 

 lateral flexor of the neck. 



Rhomboideus Minor — Origin. — ^The lower part of the ligamentum 

 nuchjE. and the spines and supraspinous ligament of the seventh 

 cervical and first thoracic vertebrae. 



Insertion.— The base of the scapula opposite the triangular 

 surface at the root of the spine. 



Rhomboideus Major — Origin. — ^The spines and supraspinous liga- 

 ments of thoracic vertebrae from the second to the fifth inclusive. 



Insertion. — ^The base of the scapula from the triangular surface 

 at the root of the spine to the inferior angle. The insertion takes 

 place by means of a tendinous expansion, which is firmly attached 

 near the inferior angle. Elsewhere the expansion is connected 

 with the base of the bone by connective tissue, so that the muscle 

 can be detached to a large extent without injury. 



Nerve-supply of the Rhomboids. — ^The nerve to the rhomboids, 

 which is a branch of the fifth cervical. This nerve, having pierced 

 the scalenus medius, gives a branch to the levator anguli scapulae, 

 and passes beneath the upper border of the rhomboideus minor 

 about I inch from the base of the scapula. Having given a branch 

 to the deep surface of that muscle, it passes beneath the rhomboideus 

 major and enters its upper part. 



The direction of the rhomboid muscles is downwards and 

 outwards. 



Action. — ^The muscles draw the scapula backwards and upwards, 

 and rotate the bone so as to depress the point of the shoulder. 



Posterior Scapular Artery. — ^This vessel is usually a branch of the 

 transverse cervical, but it may arise from the third part of the sub- 



