292 THE MUSCLES 



deeply, the spleniiis colli, the cervicalis ascendens, the serratus posticus superior, 

 and the posterior scapular vessels. 



Variations. — The number of corviciil vertebra) from which the muscle arises varies, and it 

 may even arise from the mastoid process or occipital bone. It may send slips to the serratus 

 ma.trnus, the serratus posticus superior, and other adjacent muscles ; occasionally also to the clavicle 

 and first two ribs. 



2 AND 3. RHOMBOIDEI 



The rhomboidei — named from their shape, which is rhom])oidal, or like a 

 parallelogram — are sometimes looked upon as a single muscle, but may be usually 

 separated into the following: — 



The rhomboideus minor, the lesser and upper of the two, is a four-sided sheet, 

 forming an elongated parallelogram. 



Origin. — The lower part of the ligamentum nuch«, the spines of the seventh 

 cervical and first thoracic vertebrae, and the supraspinous ligament between them. 



Insertion. — The vertebral border of the scapula opposite its spine. 



Structure. — Its origin and insertion are by short tendinous fibres, between 

 which its fleshy fibres run parallel to one another, downwards and outwards. 



Nerve-supply. — From the brachial plexus by a branch of the fifth cervical 

 nerve, which enters its deep aspect near the upper border a short distance above its 

 insertion. 



For action and relations, see the account of the following muscle. 



The rhomboideus major — the lower and larger of the two muscles — is a broad 

 rhoml)()idal sheet. 



Origin. — The spines of the four or five upper thoracic vertebrae, and the supra- 

 spinous ligament between them. 



Insertion. — The vertebral border of the scapula opposite the infraspinous fossa. 



Structure. — At the origin, it consists of short tendinous fibres, succeeded by 

 parallel fleshy bundles, which pass downwards and outwards to a narrow tendinous 

 expansion which is feebly attached to the scapula over the upper three-fourths of 

 its insertion, but with thick and strong fibres near the inferior angle of that bone. 



Nerve-supply. — The same as the preceding, and entering the upper part of 

 the deep surface near its insertion. 



Action. — The rhomboidei draw the scapula inwards and backwards towards 

 the middle line, and at the same time upwards. They also rotate the scapula so as 

 to depress the point of the shoulder. In this way they, together with the levator 

 angidi scapuhe, will help in drawing down the arm, after it has been elevated 

 through the rotation of the scapula by the trapezius and serratus magnus. 



Acting from the scapula, the rhomboidei will help the trajjczius in drawing the 

 middle line of the back towards that bone. 



Relations of the two rhomboidei. — Superficially, the trapezius and, at the 

 lower part of the rhomljoideus major, the deep fascia, and latissimus dorsi; deeply, 

 the serratus posticus superior, splenius colli, the external intercostals, the posterior 

 scapular vessels, the angles of the upper ribs, and the vertebral ai)oneurosis cover- 

 ing the upper continuations of the erector spinse. 



Variations. — The rhomboideus minor is frequently absent, and occasionally there is no rhom- 

 boideus major. The fit>res of the latter muscle may be inserted almost entirely into the lower 

 angle of the scapula. Occasionally its lower fibres join those of the latissimus dorsi, and they 

 have also heeu found continuous with a part of the teres major. An accessory band may join the 

 rhomboidei from the occipital bone (the occiiiito-scapularis). 



4. LATISSIMUS DORSI 



The latissimus dorsi Cfigs. 202 and 209) — named from its being tlic broadest of 

 the back nmsclcs — is a t'an-shaj^ed sheet forming a right-angled triangle, the right 

 angl(^ being contained between its upper and vertebral borders. 



Origin. — (1) The five or six lower thoracic spines, and the supraspinous liga- 



