290 A MANUAL OF ANATOMY 



Origin. — (i) The lower two-thirds of the ligamentum nuchae, and 

 (2) the spines of the last cervical and first six thoracic vertebrae. 



Insertion — (a) Splenius Capitis. — (i) The lower part of the outer 

 surface of the mastoid process of the temporal bone, and (2) the 

 occipital bone below the outer third of the superior curved line, in 

 each case under cover of the sterno-cleido-mastoid. (b) Splenius 

 Colli. — ^The posterior tubercles of the transverse processes of the 

 first two or three cervical vertebrae, internal to the levator anguli 

 scapulae, and in line with the cervicalis ascendens. 



Nerve-supply. — ^The posterior primary divisions of the cervical 

 nerves below the third, and of the upper five thoracic. 



The direction of the fibres is upwards and outwards. 



Action. — The muscle extends the head and flexes the neck to its 

 own side, the face being turned to the same side. 



Erector Spinae. — This composite muscle is single below in the 

 region between the last rib and iliac crest, where it is strongly 

 tendinous internally, and fleshy externally. It subsequently, how- 

 ever, resolves itself into three columns — outer, middle, and inner, 

 there being three muscles in each of the outer and middle columns, 

 and one in the inner column, thus making seven muscles in all. 



Origin. — (i) The spines of the last two thoracic, all the lumbar, 

 and the upper four sacral vertebrae ; (2) the back of the fourth 

 sacral vertebra ; (3) the posterior sacro-iliac ligament ; and (4) the 

 posterior fifth of the iliac crest. The insertion of the muscle is 

 represented by the columns into which it divides. On approaching 

 the last rib it presents a groove on its surface, which indicates its 

 division at this stage into an outer and inner column, the latter 

 representing the combined middie and inner columns. 



Outer Column. — ^This column is composed of three muscles, which, 

 from below upwards, are named ilio-costalis, musculus accessorius 

 ad ilio-costalem, and cervicalis ascendens. 



Ilio-costalis. — ^This is the direct continuation of the outer part 

 of the erector spinae, and it is inserted by fleshy and tendinous 

 bundles into the angles of ribs from the seventh to the eleventh, 

 and into the lower border of the twelfth rib. 



Musculus Accessorius ad Uio-costalem. — This muscle prolongs 

 the ilio-costalis from the lower six to the upper six ribs. It arises 

 by tendons, internal to the slips of insertion of the ilio-costalis, 

 from the angles of ribs from the seventh to the eleventh, and from 

 the outer surface of the twelfth rib, and it is inserted by tendons 

 into the angles of the upper ribs from the second to the sixth, and 

 into the outer border of the first rib external to the tubercle. 



Cervicalis Ascendens. — ^This continues the musculus accessorius 

 from the upper ribs to the neck. It arises by tendinous slips from 

 the third, fourth, fifth, and sixth ribs, internal to the tendons of 

 insertion of the musculus accessorius, and it is inserted into the 

 posterior tubercles of the transverse processes of the fourth, 

 fifth, and sixth cervical vertebrae, where it is in line with the 

 splenius colli. 



