MUSCLES OF THE HEAD AXD NECK 425 



Nerve-supply. — The suboccipital, Avhicli sends branches to its upper lx)rder. 



Action. — Chietly to rotate the atlas, and with it the head, to the same side. It 

 will also help in extension and lateral flexion of the atlas upon the axis. 



Relations. — Behind, the coniplexus and the great occipital nerve, which winds 

 round its lower border; in front, the posterior atlanto-axial ligament and vertebral 

 artery. 



4. OBLIQUUS CAPITIS SUPERIOR 



The obliquus capitis superior (fig. 308) — named from its direction and position 

 — is flat and triangular. 



Origin. — The back of the upper surface of the transverse process of the atlas. 



Insertion. — The impression immediately behind the outer half of the inferior 

 nuchal line of the occipital bone. 



Structure. — Of fleshy fibres which diverge fauAvise upwards and inwards. 



Nerve-supply. — The suboccipital, which supplies it at the inner part of its 

 deep surface. 



Action. — To extend and slightly to flex laterally the head. 



Relations. — Behind, the complexus and splenius capitis; in front, the rectus 

 capitis posticus major, vertebral artery, and posterior occipito-atlantal ligament. 



5. RECTUS CAPITIS LATERALIS 



The rectus capitis lateralis (fig. 316) — named from its direction and position 

 — is a quadrilateral sheet, and corresponds to the intertransversales posteriores of 

 the vertebrae below. 



Origin. — The front of the upper surface of the lateral mass of the atlas. 



Insertion. — The under surface of the jugular process of the occipital bone. 



Structure, — Fleshy, with parallel vertical fibres. 



Nerve-supply. — The anterior branch of the first cervical nerve which passes 

 out internal to it, and supplies it from the front. 



Action. — To flex the head laterally. 



Relations. — In front, the anterior primary branch of the first cervical nerve, 

 and the internal jugular vein; behind, the obliquus superior and the trachelo- 

 mastoid. 



Variations. — Occasionally the short muscles of this group are double. Small slips of muscle 

 have been observed, ininning from the spines of the lower cen'ical vertebrae, or the ligamentum 

 nuchae to the occipital bone. 



MUSCLES OF THE HEAD AND NECK 



The superficial layer in this region is peculiar in that it consists of numerous 

 muscles containecl in the connective tissue outside the deep fascia. This connective 

 tissue, the superficial fascia, is moderately provided Avith fat, and extends without 

 any deep connection to the adjacent regions of the thorax, arm, and back. In the 

 scalp it is firm and difficult to dissect on account of numerous septa Avhich pass 

 through it to unite the skin to the subjacent muscular aponeurosis. In this situa- 

 tion the superficial fascia is richly provided Avith blood l)y vessels Avhich run Avithin 

 it instead of beneath the deep fascia, Avhich is their usual i)ositi()n in other parts of 

 the body. 



Besides the peculiarity of their position outside tlie deep fascia, these muscles 

 are all associated in their function, A'iz. to produce the various movements of the 

 features by Avhich the expression of the emotions is effected. They are also 



