272 ANATOMY IN A NUTSHELL. 



cervical and first, second, third, and fourth dorsal vertebrae, (3) supraspinous 

 ligament. 



Insertion. — Into the upper borders of the second, third, fourth, and fifth 

 ribs beyond their angles. 



Action. — To assist in inspiration by raising the ribs into which it is in- 

 serted. 



\i:i;\ i: Supply. — External divisions of the posterior branches of the spinal 

 nerves. 



Blood Supply. — The muscles in the back are supplied by (1) occipital, 

 (2) vertebral, (3) intercostal, (4) subclavian (thyroid axis), (5) lumbar arter- 

 ies. This applies to all the muscles in the back. 



Serratus posticus inferior. — Description. — This muscle takes its name 

 from its serrated edge and its position. More than half of this muscle is apon- 

 eurosis, which blends with the posterior layer of the lumbar fascia. Its outer 

 portion is fleshy. 



Origin. — (1) Spinous processes of the eleventh and twelfth dorsal, and 

 first, second, and third lumbar vertebrae, (2) supraspinous ligament. 



Insertion. — Into the lower borders of the ninth, tenth, eleventh, and 

 twelfth ribs beyond their angles. 



Action. — It assists in inspiration by depressing the lower ribs, and making 

 them a fixed point so the diaphragm can contract. 



Nerve Supply. — External divisions of the posterior branches of the spinal 

 nerves. The nerve supply of the remaining muscles of the back is given in 

 the first part of this lesson. 



Splenius capitis and Splenius colli. — Description. — This is a broad muscle 

 which divides above into two portions for insertion. It takes its name (band- 

 age) on account of it holding down the Complexus and other muscles. 



Origin. — This muscle has one origin and two insertions and may be called 

 two muscles. (1) Lower one-half of the ligamentum nuchas, (2) spinous pro- 

 cesses of the seventh cervical, and upper six dorsal vertebrae, (3) supraspinous 

 ligament. 



Insertion. — (Capitis portion). (1) mastoid process of temporal bone, 

 (2) occipital bone beneath the superior curved line. (Colli portion) into the 

 transverse processes of the first, second, and third cervical vertebra? (posterior 

 tubercles. I 



Action.— It flexes the head and neck, laterally, extends them, and rotates 

 the face to same side. 



LESSON LXXVI. 



Muscles of the Fourth Layer of the Back. 

 Erector Spinae. — Description. — This muscle and its continuations fill up 

 the vertebral groove on each side of the spine. In the sacral region this muscle 

 is primed and tendinous. In the lumbar region it is larger and fleshy. In 

 the dorsal region it divides into its branches, and these sub-divide. This 

 muscle is covered in the lumbar region bythe lumbar fascia; in the dorsal region 



