198 MYOLOGY. 



TRIANGULARIS STERNI. 

 (Sterno-cos tails. ) 



Situated in the thorax and upon the sternum, it is triangular, 

 tendinous, and dentated on its outer border. 



Origin. From the superior sternal ligament and segments. 



Insertion. To the cartilages, and inner surfaces of the distal 

 ends of the true ribs, excepting the first. 



Action. To assist in expiration. 



DORSO-LUMBAR REGION. 



The muscles of this region, a single group, are closely related 

 with the superior aspect of the vertebral column, and we describe 

 them as consisting: of four 



Longissimus dorsL 

 Spinalis dorsi. 



Semispinalis dorsi et lumborum. 

 Intertransversales lumborum. 



LONGISSIMUS DORSL 

 (Ilio-spinalis.) 



(PL. III. 14.) 



Situated on the superior part of the back and loins, this, the 

 longest and most powerful muscle in the body, occupies the space 

 between the costal angles and the dorso-lumbar spines ; broad 

 and fleshy at its origin in the loins, it becomes deeper and 

 narrower as it proceeds forwards. Towards the withers it diverges, 

 presenting three distinct portions, two of which proceed in an 

 oblique direction to the neck, and terminate by several tendons 

 (the deeper portion is described as the spinalis dorsi) ; the third 

 portion is adherent to the sides of the anterior dorsal spines. The 

 belly of this muscle is intersected by several tendons, and is 

 invested posteriorly by a very strong, tendinous aponeurosis. 



Attachments. The crest, inner surface, and supero-anterior 

 spine of the ilium ; the spinous and transverse processes of the 

 first two bones of the sacrum ; the spinous, transverse, and 

 oblique processes of all the lumbar vertebrae ; the spinous and 

 transverse processes of all the dorsal vertebras ; the external 

 surface of the last fifteen or sixteen ribs just above the trans- 

 versalis costarum, and the spinous and transverse processes of 

 the last three or four cervical vertebrae. 



