424 THE MUSCLES 



Nerve-supply. — The spinal nerves as they emerge from the mtervertebral for- 

 amina. 



Action. — To Hex laterally the spinal column. 



Relations. — In the neck, the anterior primary branches of the nerves come 

 out l)et\veen the anterior and })osterior intertransversales, and the posterior primary 

 branches emerge at the inner borders of the posterior intertransversales. They are 

 hidden from view l\v the mass of muscles attached to the transverse processes. In 

 the lumbar region they lie under cover of the erector spinse and its divisions, and 

 they are covered in front by the psoas (fig. 286). 



THE SUBOCCIPITAL MUSCLES 



The suboccipital group consists of short muscles, situated in the same plane as 

 the preceding, but somewhat altered in their arrangement on account of the })eculiar 

 movements of the region. They are the rectus capitis posticus major and minor, 

 the obliquus capitis inferior and superior, the rectus capitis lateralis. 



1. RECTUS CAPITIS POSTICUS MAJOR 



The rectus capitis posticus major (fig. 308) — somewhat incorrectly named 

 from the direction of its fil)res, its position, and size — is a triangular sheet. 



Origin. — The upper surface of the spine of the axis along its side and one-half 

 of its bitid tip. 



Insertion. — The middle third of the inferior nuchal line of the occipital bone. 



Structure. — From a narrow tendinous origin the fleshy fi1)res diverge as they 

 run upwards and outwards to a broad insertion. 



Nerve-supply. — A branch of the suboccipital which enters the middle of its 

 superficial surface. 



Action. — To extend the head upon the neck; and to rotate the head to the 

 same side. 



Relations. — Behind, the complexus and obliquus superior; in front, the 

 succeeding muscle. 



2. RECTUS CAPITIS POSTICUS MINOR 



The rectus capitis posticus minor (fig. 308) — named from its direction, size, 

 and position — is also flat and triangular. 



Origin. — The upper part of one-half of the posterior tubercle of the atlas. 



Insertion. — The inner third of the inferior nuchal line of the occipital bone, 

 and the s})ace immediately in front of it. 



Structure. — Fleshy, and consisting of fibres which diverge in fan shape as they 

 pass upwards and outwards. 



Nerve-supply. — Branches of the suboccipital nerve which enter the outer part 

 of its su}K'rficial surface. 



Action. — To extend the head on the neck. 



Relations. — Behind, the preceding muscle and complexus; in front, the pos- 

 terior occipito-atlantal ligament. 



3. OBLIQUUS CAPITIS INFERIOR 



The obliquus capitis inferior (fig. 308)— uanud from its direction and 

 position — is a fusiform sheet. 



Origin. — The up])er })art of the side of tb(^ spine of the axis. 



Insertion. — The lower part of the ti]) of the transverse process of the atlas. _ 



Structure. — Strong and fleshy, with pointed extremities, and a general direc- 

 tion upwards and outwards. 



