278 ANATOMY IN A NUTSHELL. 



Origin. — Spinous process and external to the process immediately above. 



Insertion. — Spinous processes immediately above. 



Action. — Approximate the spinous processes. 



Interspinales. — Description. — These muscles are six pairs in the cervical 

 region (first pair between axis and third cervical.) They are in the upper and 

 lower dorsal, but absent in the middle dorsal. There are four pairs between 

 the five lumbar vertebrae, sometimes one above and one below these pairs. 



Origin. — Spinous process below. 



Insertion. — Spinous process above. 



Action. — Approximate the spinous processes. 



Intertransversales. — Description. — In the cervical region these are best 

 developed, and are in pairs (anterior and posterior) passing between the anter- 

 ior and posterior tubercles of the tranverse processes. Between these muscles 

 pass the anterior division of the spinal nerve. There are seven pairs in the cer- 

 vical region. 



In the dorsal region they are not well developed. They are absent in the 

 middle dorsal. In the lumbar region they are in pairs — one set called the 

 intertransversales laterales, which are situated between the transverse pro- 

 cesses. The other set called intertransversales mediales are situated between 

 the accessory process of one vertebra and the mammillary process of the next. 



Origin. — In a transverse process below. 



Insertion. — Transverse process immediately above. 



Action. — Approximate the transverse processes. 



Extensor coccygis. — Description. — This muscle extends over the lower 

 part of the posterior surface of sacrum and coccyx. 



Origin. — Last sacral or first coccygeal vertebra. 



Insertion. — Lower part of the coccyx. 



Action. — To extend the coccyx. 



Rectus capitis posticus major. — Description. — This muscle becomes broad 

 as it ascends. 



Origin. — Spinous process of axis. 



Insertion. — Inferior curved line of the occipital bone and surface of bone 

 below. 



Action. — To rotate the cranium with atlas, around the odontoid process 

 of the axis. 



Rectus capitis posticus minor. — Description. — This muscle is the smallest 

 of the muscles in this region. 



Origin. — Tubercle on posterior arch of atlas. 



Insertion. — Occipital bone beneath the inferior curved line. 



Action. — To draw the head backward. 



Obliquus capitis superior. — Description. — This muscle is narrow below 

 but wide above. 



Origin. — Upper surface of transverse process of atlas. 



Insertion. — Occipital bone between the superior and inferior curved lines 

 external to the Complexus. 



ACTION. — To draw the head backward and rotate cranium. 



