SHORT CRANIO-VERTEBRAL MUSCLES. 305 



connected one to each of the two parts into which the spinous process 

 is divided. In the dorsal part of the column only a few are met with, 

 and these are not constant. 



Varieties. — The sjnnalis cervicis consists of a few in'egTilar bundles of fibres 

 or greater length than the preceding- muscles, placed close to the ligamentum 

 nuchas : they arise by two or more heads from the spines of the fifth and sixth 

 ceiTical and sometimes other neighbom-ing vertebra?, and are inserted into the 

 spine of the axis, and occasionally into the two vertebras next below it. This 

 muscle is sometimes wanting. (See Henle and Heilenbeck, in luiUler's " Ai-chiv," 

 1837.) 



The name sacro-coccyge^is 2}('stic'iis, or extensor coceijgis, has been given to 

 slender fibres occasionally found extending from the lower end of the sacrum to 

 the coccyx, and representing the extensor of the caudal vertebrae of other 

 animals. (Gixnther and Milde, '• Chirurgische Muskellehre," quoted by Theile, 

 " Sommening vom Baue," &;c.) 



Short Posterior Cranio-Vertebral Muscles. — The rectus 

 capitis posticus major muscle arises by a narrow tendon from the 

 spinous process of the axis, and expanding as it passes upwards and 

 outwards, is inserted into and beneath the outer part of the inferior 

 curved line of the occipital bone. Its insertion is inside and below 

 that of the superior oblique muscle. 



The rectus capitis posticus minor muscle arises from the posterior 

 arch of the atlas by the side of the tubercle, and expands as it passes 

 to be inserted into the inferior curved line of the occipital bone, and 

 the rough surface between that and the foramen magnum. 



The obliquus capitis inferior, the strongest of the muscles now 

 under consideration, arises from the spinous process of the axis, between 

 the origin of the rectus posticus major and the insertion of the semi- 

 spinalis colli, and is inserted into the extremity of the transverse 

 process of tlie atlas. 



The obliquus capitis superior, smaller than the preceding muscle, 

 arises from the upper surface of the transverse process of the atlas, 

 inclines from thence obliquely upwards and backwards, increasing some- 

 what as it ascends, and is inserted into a groove situated externaUy to 

 the inferior curved line of the occipital bone. 



Melations. — The two oblique muscles with the rectus major, fomi the sides of 

 a small triangular space, in the area of which the posterior primary branch of 

 the sub-occipital nerve and the vertebral artery will be found. 



Nerves. — All the muscles of the back which are unconnected with the upper 

 limb, viz., the posterior sen-ati, splenius, complexus, erector spina;, and the muscles 

 more deeply seated ai-e supplied by the posterior primary branches of the spinal 

 nerves. 



Actions. — The transverso-spinales muscles, including the complexus, are cssen» 

 tially extensors of the head and vertebral column ; and the movements produced 

 by them vary according as the muscles of one side or both are in action, in a 

 manner similar to that already pointed out in regard to the erector muscles. 



The interspinales and intertransversales muscles approximate the vertebra 

 between which they pass, and thus may act as extensors and lateral flexors 

 respectively of the portion of the vertebral column in which they are situated. 



Of the four muscles last described, two — the rectus minor and superior oblique 

 — act piincipally by di-awing the head backwards, that being the chief movement 

 allowed between the atlas and occipital bone ; while the principal action of the 

 rectus posticus major and the inferior oblique, when acting on one side, is to 

 rotate the atlas and skull upon the axis, 



VOL. I. X 



