5IO HUMAN ANATOMY. 



crest are mainly inserted into the lower six or seven ribs, and form what is termed the 

 ilio-costalis lumborum. With the remainder of the iliac fibres bundles arising from 

 the lower five, six, or seven ribs associate themselves to form the ilio-costalis dorsi. 

 also termed the accessorius, which inserts into the upper five or six ribs ; and, finally, 

 the uppermost portion of the muscle, the ilio-costalis cervicis or cervicalis ascendens, is 

 formed by the union of bundles arisi?ig from the upper six or seven ribs, and is m- 

 serted into the posterior tubercles of the transverse processes of the fourth, fifth, and 

 sixth cervical vertebrae. 



Nerve-Supply. — From the posterior divisions of the spinal nerves from the 

 lower cervical to the first lumbar. 



Action. — The various portions of the ilio-costalis tend to bend the spinal 

 column backward in the lower cervical, thoracic, and lumbar regions, and also to 

 draw it somewhat to one side. They may likewise have some action in drawing 

 down the ribs, assisting in forced expiration. 



3. LoNGissiMUS (Fig. 520). 



Attachments.— The longissimus represents the upward prolongation of that 

 portion of the sacro-spinalis which arises from the dorso-lumbar fascia and the 

 lumbar vertebrae. It is continued upward immediately medial to the ilio-costalis to 

 be inserted into the mastoid process of the temporal bone, but, like the ilio-costalis, 

 it receives in its course accessory bundles and also gives off bundles which are 

 inserted into the skeletal parts over which it passes. 



The fibres which represent the direct continuation of the sacro-spinalis are con- 

 tinued as far upward as the first thoracic vertebra, and are reinforced by short acces- 

 sory bundles from the transverse processes of the lower six thoracic vertebrae to form 

 what is termed the longissimus dorsi. The fibres of this portion of the muscle are 

 inserted along two lines, the medial of which passes along the accessory processes of 

 the lumbar vertebrae and the transverse processes of all the thoracic vertebrae, while 

 the lateral line passes along the transverse processes of the lumbar vertebrae and the 

 angles of the ribs as far forward as the second. From the transverse processes of 

 the upper six thoracic vertebrae bundles arise which unite to form the longissimus 

 cervicis or transversalis cervicis, which continues the line of the longissimus to an 

 insertion into the posterior tubercles of the transverse processes of the second to 

 the sixth cervical vertebrae ; and, finally, the longissimus capitis or trachelo-mastoid 

 is formed by bundles arising from the transverse processes of the three upper 

 thoracic vertebrae and the articular processes of the three lower cervical, and passes 

 upward to be inserted into the mastoid process of the temporal bone. 



Nerve-Supply, — From the posterior divisions of the spinal nerves from the 

 third cervical to the second sacral. 



Action. — The thoracic and cervical portions of the longissimus will draw the 

 spinal column backward and to one side ; the longissimus capitis will have a similar 

 action on the head. 



4. Splenius (Fig. 520). 



Attachments. — The splenius forms a fiat muscle which arises from the spinous 

 processes of the upper four or six thoracic and the seventh cervical vertebrae and 

 from the lower half of the ligamentum nuchae. It passes upward and slightly 

 laterally and divides into two portions, the lower of which, curving around the outer 

 edge of the upper portion, passes to an i7isertion in the posterior tubercles of the 

 upper three cervical vertebrae, forming the splenius cervicis. The upper portion, 

 which is termed the splenius capitis^ continues upward, and is inserted by a short 

 tendon into the posterior border of the mastoid process of the temporal bone and 

 into the outer part of the superior nuchal line. 



Nerve-Supply. — From the posterior divisions of the second to the eighth cer- 

 vical nerves. 



Action.- — The splenius cervicis will draw the upper cervical vertebrae backward 

 and will rotate the atlas towards the side of the muscle in action. The action of 



