370 DISSECTION OF THE BACK. 



This muscle is concealed by the complexus and trachelo-mastoideus, and 

 crosses the vertebral artery. Its insertion is beneath the splenius (E), but 

 above the rectus major muscle. 



Action. With its fellow the upper oblique will assist in carrying back- 

 wards the head. By the action of one muscle the occiput will be inclined 

 backwards to the same side. 



The SEMISPINALIS (fig. 119, G) occupies the vertebral groove in the 

 dorsal and cervical regions, and extends from the transverse and articular 

 processes to the spines of the vertebra? ; it is undivided at the outer, but 

 bifurcated at the inner attachment. It arises externally from the trans- 

 verse processes of the ten upper dorsal vertebrae, and from the articular 

 processes of the four lower cervical ; and it is inserted by two pieces, as 

 below : 



The lower piece, semispinalis dorsi, is inserted into the spinous processes 

 of the upper four dorsal and the last two cervical vertebras. 



The upper piece, semispinalis colli, is inserted into the spines of the 

 cervical vertebras above the attachment of the semispinalis dorsi, the atlas 

 not receiving any slip. 



The semispinalis muscle is covered by the complexus, and the deep cer- 

 vical artery. Some of the cervical nerves are superficial, and others 

 beneath it. To its inner side is the multifidus spinas muscle. 



Action. The muscles of both sides acting together will extend the spine. 

 One muscle will rotate the cervical and dorsal parts of the spine, so as to 

 turn the face to the opposite side. 



* The INTERSPINAL MUSCLES are placed, as their name expresses : they 

 are arranged in pairs, one on each side of the interspinous ligament ; and 

 they are best seen in the neck and loins. 



In the cervical region the muscles are absent from the interval between 

 the first two vertebras. They are small round bundles, and are attached 

 above and below to the bifurcated apices of the spines. 



* In the dorsal region the muscles are rudimentary ; they exist between 

 the first two, and the lowest two pair of spinous processes, and between 

 the last dorsal and the first lumbar vertebra. 



* In the lumbar region they are thin flat muscles, which reach the 

 length of the spines. 



Action. By the approximation of the spinous processes these small 

 muscles will help in extending the spine. Necessarily the movement of 

 each pair is very slight, but the aggregate of all would amount to percep- 

 tible motion. 



* The INTERTRANSVERSE MUSCLES lie between the transverse pro- 

 cesses of the vertebras ; but only those in the loins and the back are now 

 dissected. 



In the neck they are double, like the interspinal muscles of the same 

 vertebras (p. 165). 



* In the dorsal region they are single rounded bundles, and are found 

 only between the lower processes : their number varies from three to six. 



* In the lumbar region the anterior set are four thin and fleshy planes. 

 The posterior set are rounded bundles, which are attached to the accessory 

 points at the roots of the transverse processes : these have been named 

 interaccessorii. 



Action. The small intertrans versa! es help to incline laterally the spine 

 by approximating the transverse processes ; the motion between a single 



