RECTI AND OBLIQUI. 369 



occipital vein lies with its artery, and communicates sometimes 

 with the lateral sinus of the skull through the mastoid foramen. 



The dorsal and lumbar veins correspond in their branching and distri- 

 bution with the arteries they accompany, and end in the intercostal veins 

 and the vena cava. 



In contact with the spinous processes and plates of the vertebrae is a 

 deeper set of veins (dorsi spinal), which anastomose freely together, and 

 open into the veins in the interior of the spinal canal. 



* FIFTH LAYER. In this layer are the following small muscles : the 

 recti and obliqui, semispinalis, interspinales, multifidus spinai, and inter- 

 transversales. 



Dissection. Most of the remaining muscles of the Back are uncovered 

 by the previous dissection. Between the Hrst two vertebra? and the occi- 

 pital bone the small straight and oblique muscles extend. 



* In the cervical and dorsal regions the semispinalis muscle appears, 

 with the small interspinales internal to it ; and occupying a corresponding 

 position in the loins, is the multifidus spinas. 



* The small intertransverse muscles of the lumbar region will be found 

 by removing the erector spinae. 



The RECTUS CAPITIS POSTicus MAJOR (fig. 119, A) is the largest of 

 the muscles between the occipital bone and the first two vertebras, and 

 arises from the side of the spinous process of the axis. It is inserted into 

 the outer part of the inferior curved line of the occipital bone for about an 

 inch, as well as into the surface below it. 



The muscle is directed outwards very obliquely, and forms one side of 

 the triangular space which contains the suboccipital nerve and the verte- 

 bral artery. Its upper attachment lies beneath the superior oblique 

 muscle. 



Action. By the action of both muscles the head will be put backwards. 

 By one rectus the face will be turned to the same side; and after the head 

 has been so rotated, the muscle will assist in extending the head. 



The RECTUS CAPITIS POSTICUS MINOR (fig. 119,n) is internal to the 

 preceding, and is shorter than it. Arising from the neural arch of the 

 atlas, the muscle is inserted, close to the middle line, into the inferior 

 curved ridge of the occipital bone, and between this and the foramen 

 magnum. 



This small muscle is fan-shaped, and is deeper than the rectus major : 

 it covers the ligament between the atlas and the occipital bone. The two 

 small recti muscles correspond with the inter-spinales between the other 

 vertebras. 



Action. Both muscles, or one, will have the same use, viz., to approach 

 the occiput to the atlas. 



The OBLIQUUS INFERIOR (fig. 119, c) slants between the first two 

 vertebras. It arises from the spinous process of the axis, external to the 

 rectus major muscle, and is inserted into the tip of the transverse pro- 

 cesses of the atlas. 



Action. One muscle turns the face to the same side by rotating the 

 atlas on the axis. If both muscles act at the same time they will assist in 

 keeping the head straight. 



The OBLIQUUS SUPERIOR (fig. 119, D) takes origin from the upper part 

 of the transverse process of the atlas, where the preceding muscle termi- 

 nates ; and is directed inwards to be inserted between the curved lines of 

 the occipital bone, near the mastoid process. 

 24 



