COSTAL REGION. 191 



Origin. — From the neural spines of the first four or five 

 dorsal vertebrse, and from their supraspinous ligament. 



Insertion. — To the inner surface of the superior costa of the 

 scapula, and to its cartilage of prolongation. 



Relation. — Externally with the cartilage of the scapula, and 

 the dorsal trapezius, and separated from the anterior portion of 

 the superficialis costarum by a thin layer of elastic tissue ; 

 anteriorly with the rhomboideus longus; posteriorly with the 

 latissimus dorsi ; internally with the splenius. 



Action, — To draw the scapula upwards. 



LATISSIMUS DORSI. 



{Dorso-humercdis. ) 



(Pl. XL 15.) 



This muscle is situated on the supero-lateral part of the chest 

 and the loins ; it is very large, flat, thick, and triangular, its 

 fibres extending obliquely downwards and forwards ; it is aponeu- 

 rotic above, fleshy below, with a tendinous and aponeurotic 

 insertion. 



Origin. — By a broad aponeurosis, from the supraspinous liga- 

 ment and spinous processes of the vertebrae, commencing about 

 the highest point of the withers, and stretching as far as the last 

 lumbar. The fleshy portion becomes thick just behind the 

 scapula, then it contracts, terminating in a flat tendon, which 

 passes under the latter. It fits in a notch at the dorsal scapular 

 angle, formed by the projection of the cartilage of prolongation, 

 which it overlaps. 



Insertion. — The internal tuberosity of the humerus, along 

 with the teres internus, and between the two insertions of the 

 coraco-humeralis. Before passing under the scapula, it gives off 

 a strong aponeurosis, which passes over the supero-posterior part 

 of the scapula, and becomes continuous with its fascia. 



Relation. — Externally with the panniculus carnosus, skin, 

 triceps extensor brachii, and dorsal trapezius ; superiorly with 

 the rhomboideus brevis and dorsal angle of the scapula ; inter- 

 nally with the ribs, serratus magnus, superficialis costarum, and 

 gluteus maximus. 



Action. — To elevate the humerus, and thus flex the shoulder- 

 joint ; it is likewise an expiratory muscle, when the limb is fixed. 



