OF THE BAfK. 439 



of two contiguous vertebrae, separated from one another by the anterior division of 

 the cervical nerve, which lies in the groove between them. In this region there 

 are seven pairs of these muscles, the first pair being between the atlas and axis, 

 and the last pair between the seventh cervical and first dorsal vertebrae. In the 

 il f>-'/io/i they are least developed, consisting chiefly of rounded tendinous 

 cords in the intertransverse spaces of the upper dorsal vertebrae ; but between the 

 transverse processes of the lower three dorsal vertebrae, and between the transverse 

 processes of the last dorsal and the first lumbar, they are muscular in structure. 

 In the lumbar region they are four in number, and consist of a single muscular 

 layer, which occupies the entire interspace between the transverse processes of the 

 lower lumbar vertebrae, whilst those between the transverse processes of the upper 

 lumbar are not attached to more than half the breadth of the process. 



The Rectus capitis posticus major arises by a pointed tendinous origin from the 

 spinous process of the axis, and, becoming broader as it ascends, is inserted into 

 the inferior curved line of the occipital bone and the surface of bone immediately 

 below it. As the muscles of the two sides pass upward and outward, they leave 

 between them a triangular space, in which are seen the Recti capitis postici 

 min ores muscles. 



Relations By its superficial surface, with the Complexus. and, at its inser- 

 tion, with the Superior oblique : by its deep surface, with part of the Rectus capitis 

 p>stictis minor, the posterior arch of the atlas, the posterior occipito-atlantal liga- 

 ment, and part of the occipital bone. 



The Rectus capitis posticus minor, the smallest of the four muscles in this 

 region, is of a triangular shape : it arises by a narrow pointed tendon from the 

 tubercle on the posterior arch of the atlas, and, becoming broader as it ascends, is 

 inserted into the rough surface beneath the inferior curved line, nearly as far as 

 the foramen magnum, nearer to the middle line than the preceding. 



Relations. By its superficial surface, with the Complexus and the Rectus 

 capitis posticus major; b\ its deep surface, with the posterior occipito-atlantal 

 ligament. 



The Obliquus capitis inferior, the larger of the two Oblique muscles, arises 

 from the apex of the spinous process of the axis, and passes almost horizontally 

 outward, to be inserted into the lower and back part of the transverse process of 

 the atlas. 



Relations. By its superficial surface, with the Complexus and with the pos- 

 terior division of the second cervical nerve, which crosses it ; by its deep surface, 

 with the vertebral arterv and posterior atlanto-axial ligament. 



The Obliquus capitis superior, narrow below, wide and expanded above, arises 

 by tendinous fibres from the upper surface of the transverse process of the atlas, 

 joining with the insertion of the preceding, and. passing obliquely upward and 

 inward, is inserted into the occipital bone, between the two curved lines, external 

 to the Complexus. 



Relations. By its superficial surface, with the Com plexus and Trachelo-mastoid. 

 By its deep surface, with the posterior occipito-atlantal ligament. 



The Suboccipital Triangle. Between the two oblique muscles and the Rectus 

 capitis posticus major a triangular interval exists, the suboccipital triangle. This 

 triangle is bounded, above and internally, by the Rectus capitis posticus major; 

 above and externally, by the Obliquus capitis superior ; below and externally, by the 

 Obliquus capitis inferior. It is covered in by a layer of dense fibro-fatty tissue, 

 situated beneath the Complexus muscle. The floor is formed by the posterior 

 occipito-atlantal ligament, the posterior arch of the atlas, and the posterior atlanto- 

 axial ligament. It contains the vertebral artery, as it runs in a deep groove on the 

 upper surface of the posterior arch of the atlas, and the posterior division of the 

 suboccipital nerve. 



Nerves. The Semispinalis dorsi and Rotatores spinae are supplied by the 

 internal branches of the posterior divisions of the dorsal nerves ; the Semispinalis 

 colli, by the internal branches of the posterior divisions of the cervical nerves : the 



