DISSECTION OF THE HEAD AND NECK. 169 



and the following muscles are to be isolated, the nerves and vessels 

 being thereafter dissected on the other side. 



The Obliquus Capitis Inferior. This muscle, the most powerful of 

 the group, covers the atlan to-axial joint on each side. It arises from the 

 superior spine of the dentata; and it is inserted into the wing of the 

 atlas on its upper aspect. 



Action. — To rotate the atlas (and head) aroimd the odontoid process 

 of the axis. 



The Obliquus Capitis Superior. This muscle covers the occipito- 

 atlantal joint on each side. It a7-ises from the free edge of the wing of 

 the atlas ; and it becomes inserted into the mastoid crest and styloid 

 process of the occipital bone. 



Action. — To extend the head on the atlas. 



The Rectus Capitis Posticus Major. This muscle is composed of 

 two parallel portions which, although not distinctly separated from one 

 another, were described as distinct muscles by Percivall. It arises from 

 the spinous process of the axis. Its most superficial fibres (complexus 

 minor of Percivall) join the occipital insertion of the complexus; while 

 its deeper portion (rectus capitis posticzis major of Percivall) is inserted 

 into the back of the occipital bone, beneath the insertion of the com- 

 plexus. 



Action.— -The same as the preceding muscle. 



The Rectus Capitis Posticus Minor. This is the smallest muscle of 

 the group. It lies beneath the preceding, and covers the occipito-atlantal 

 joint. It arises from the upper aspect of the ring of the atlas; and it is 

 inserted into the back of the occipital bone, beneath the last-described 

 muscle. 



Action. — The same as the two preceding muscles. 



The 1st Cervical Nerve (Suboccipital of man) issues from the spinal 

 canal by the antero-internal foramen of the atlas. At its point of 

 emergence it resolves itself into superior and inferior primary branches. 

 The latter is immediately directed down through the antero-external 

 foramen, and will be followed at a later stage. The superior primary 

 branch appears between the obliquus capitis superior and the rectus 

 capitis posticus muscles, where it gives (1) muscular branches to these 

 muscles, and (2) auricular branches already followed to the skin of the 

 ear. 



The 2nd Cervical Nerve issues by the foramen at the anterior edge of 

 the arch of the axis, where it is covered by the obliquus capitis inferior. It 

 divides into superior and inferior primary branches, the latter of which 

 has already been referred to (page 144). The superior branch gives twigs 

 to the superior and inferior oblique muscles of the head, and is 

 continued like the succeeding members of the cervical series (page 154). 



The Occipital Artery. This vessel will be found ascending through 



