iMUSCLES OF THE BACK AND LOINS 323 



superior spines of the dorsal vertebrae from the 3rd to the 10th, whence 

 its fibres pass downward and forward. 



Insertion. — Into the tubercle on the outside of the spine of the scapula. 



Action. — The cervical or neck portion acting alone would pull the 

 shoulder upwards and forwards. The dorsal or back division acting alone 

 would draw it upwards and backwards. 



Latissimus Dorsi. — A Hat, triangular muscle spread over the back 

 and loins, where it commences in a broad aponeurotic tendon. It extends 

 obliquely downward and forward over the side of the chest, and, gradually 

 becoming narrower, passes between the fore-limb and the trunk to reach 

 the humerus or upper arm bone. 



Origin. — From the superior spines of all the lumbar and the fourteen 

 posterior dorsal vertebrae. 



Insertion. — By a short tendon into a small tubercle on the internal 

 surface of the humerus or upper arm bone. 



Action. — To Hex the humerus on the scapula and incline the leg towards 

 the trunk. 



Serratus Anticus. — Situated on the side of the chest. The serratus 

 anticus consists of a number of fleshy slips, whose fibres are directed back- 

 wards and end above in a flat aponeurotic tendon. 



Origin. — From the 2nd to the 13th dorsal spines. 



Insertion. — Into the anterior borders and outer surfaces of all the ribs 

 from the 5th to the 13th. 



Action. — By drawing the ribs forwards and upwards it enlarges the 

 chest and assists in inspiration. 



Serratus Posticus. — Situated behind the one last described, of which 

 it seems to be a continuation. It is composed of a flat or aponeurotic 

 tendon and a number of fleshy segments. 



Origin. — From the spinous processes of the seven posterior dorsal 

 vertebrae and the two anterior lumbar. 



Insertion. — Into the outer surfaces and posterior borders of the eight or 

 nine last ribs. 



Action. — To pull the ribs backwards and assist in expiration. 



Longissimus Dorsi. — This is the longest, the largest, and most 

 powerful muscle in the body. It is situated on the arches of the ribs, 

 in close connection with the spines of the dorsal and lumbar vertebras, 

 and extends from the ilium behind, over the loins and the back to the 

 fourth cervical vertebra in front. 



Origin. — From the internal surface and anterior border of the ilium 

 or haunch bone, and the ligament (sacro-iliac) connecting it with the 

 sacrum, and from the sacral bone. ' ' 



