492 MUSCLES ON POSTERIOR NECK AND BACK. 



back part of the chest, arises -"by a thin aponeurotic tendon, 

 from the ligamentum nuchee, the three inferior spines of 

 the neck, and from the two or three superior spines of the 

 back, and is inserted lay fleshy digitations into the upper 

 edges of the second, third, and fourth ribs. 



Function. To elevate the ribs, and thus, by expanding 

 the chest, to assist in inspiration. 



The serratus posticus inferior, situated at the lower and 

 back part of the chest,, is a broader and thinner muscle 

 than the last. It arises, by a very delicate tendinous ex- 

 pansion, beneath the latissimus dorsi, with which it is 

 strongly connected, through the fascia lumborum; from 

 the spinous processes of the two lower dorsal, and two or 

 three upper lumbar vertebra?, and is inserted, by fleshy 

 digitations, into the inferior margins of the four lower ribs, 



Function. To depress the ribs, and thus by lessening 

 the capacity of the chest, to assist in expiration. It is the 

 antagonist muscle of the superior serratus. 



The splenius capitis et colli has its lower portion con- 

 cealed by the muscle before the last ; and its upper, by the 

 trapezius. It arises from the four or five superior spines of 

 the back, and the three or four lower of the neck, and from 

 the ligamentum nucha?; it ascends as a long, flat, and 

 fleshy muscle, and is inserted, by two distinct portions one 

 for the head into the mas toid process of the temporal bone, 

 and the surface between the two semicircular ridges of the 

 occipital ; and the other, for the neck, into the transverse 

 processes of the two or three superior cervical vertebra?. 



Function. To bend the head and neck backward. 



The fourth layer is seen by removing the serrati and 

 splenii, and consists of the following seven muscles : 



Sacro-lumbalis , longissimus dorsi, spinalis dorsi. These 

 three muscles are associated under the name of erector spinw. 

 The whole appear as one mass, occupying the space between 

 the spinous processes and the angles of the ribs. 



The first two have a common origin from the posterior 

 surface of the sacrum, from the posterior third of the crest 

 of the ilium, and from the spinous and oblique processes of 



