i8o HEAD AND NECK 



not been retained, by endeavouring to find the twig which it gives to the 

 rectus capitis posterior major. The tissue in which the nerve lies is very 

 dense, and the dissection is in consequence somewhat difficult. 



Rectus Capitis Posterior Major. This muscle springs by a 

 pointed origin from the spine of the epistropheus (O.T. axis), 

 and, expanding as it passes upwards and laterally, it is inserted 

 into the occipital bone along the lateral portion of the inferior 

 nuchal line and the surface immediately below. 



Rectus Capitis Posterior Minor. This is a small fan- 

 shaped muscle, placed to the medial side of, and overlapped 

 by, the preceding muscle. It takes origin from the tubercle 

 on the posterior arch of the atlas, and is inserted into the 

 medial part of the inferior nuchal line of the occipital bone 

 and the surface between this and the foramen magnum. 



Obliquus Capitis Inferior. This muscle extends from the 

 extremity of the spine of the epistropheus to the posterior 

 border of the transverse process of the atlas. The great 

 occipital nerve will be seen hooking round its lower border. 



Obliquus Capitis Superior. This muscle springs from 

 the transverse process of the atlas, and is inserted into 

 the occipital bone in the interval between the nuchal lines, 

 below and to the lateral side of the semispinalis capitis. 



Posterior Branch of the Sub -Occipital Nerve. The 

 posterior branch of the sub-occipital nerve does not divide 

 into medial and lateral divisions. It enters the sub-occipital 

 triangle by passing dorsally, between the posterior arch of 

 the atlas and the vertebral artery, and at once breaks up 

 into branches which go to supply five muscles viz. the two 

 posterior recti, the two oblique muscles, and the semispinalis 

 capitis. In addition to these muscular twigs it gives a com- 

 municating^ and sometimes a cutaneous filament. 



The communicating branch generally proceeds from the 

 nerve to the obliquus capitis inferior, and joins the great 

 occipital nerve. The cutaneous branch, when present, accom- 

 panies the occipital artery to the integument over the occiput. 



Arteria Vertebralis. Only the third portion of this vessel 

 lies in the sub-occipital triangle. Emerging from the foramen 

 in the transverse process of the atlas, it runs posteriorly and 

 medially in the groove upon the posterior arch of the same 

 bone. In this course it lies immediately posterior to the lateral 

 mass of the atlas and above the sub-occipital nerve. It leaves 

 the space by passing anterior to the thickened lateral ex- 



