THE DISSECTION OF THE BACK 65 



portion of the longissimus springs from the transverse processes of the upper 

 four thoracic vertebroe, and is inserted into the posterior tubercles of the 

 transverse processes of the cervical vertebrae from the second to the sixth 

 inclusive. 



Longissitmts Capitis (O.T. Trachelo-mastoid). The longissimus capitis 

 lies in the neck, under cover of the splenius. It arises, in common with the 

 longissimus cervicis, from the transverse processes of three or four of the upper 

 thoracic vertebrae, and, in addition, from the articular processes of a like 

 number of the lower cervical vertebrae. Thenarrow, fleshy band which results 

 is inserted into the posterior part of the mastoid portion of the temporal 

 bone, under cover of the splenius capitis and sterno-mastoid muscles. 



Musculus Spinalis. The spinalis muscle is the most medial, shortest, 

 and weakest of the three columns, and the most difficult to define. Below, 

 it is intimately blended with the longissimus dorsi, but it may be regarded 

 as taking origin by four tendons from the spines of the upper two lumbar 

 and lower two thoracic vertebrae. The tendons end in a small muscular 

 belly, which is inserted by a series of slips into a very variable number of 

 the upper thoracic spines. It is closely connected with the subjacent semi- 

 spinalis dorsi. 



Spinalis Cervicis. This upward prolongation of the spinalis is not 

 always easy to define. It springs from the spines of the lower four cervical 

 vertebras and is inserted into the spines of the second, third, and fourth 

 cervical vertebrae. 



The various segments of the sacro-spinalis are supplied by the posterior 

 rami of the spinal nerves. When the segments on one side only act they 

 bencl the vertebral column to that side, but when the segments on both 

 sides act simultaneously they bend the vertebral column backwards. 



Dissection. The occipital artery has already been seen 

 crossing the apex of the posterior triangle (p. 36), and its 

 terminal branches have been dissected as they ramify in the 

 scalp (p. 55). To expose the second part of the vessel, which 

 extends from under shelter of the mastoid process, along the 

 superior nuchal line of the occipital bone, to the point where it 

 pierces the trapezius to become superficial, divide the longissimus 

 capitis (O.T. trachelo-mastoid) a short distance below its inser- 

 tion, and throw it upwards as far as possible, along with the 

 splenius capitis; then clean the artery. 



Arteria Occipitalis. In the region of the mastoid process 

 the second part of the occipital artery is very deeply placed ; 

 indeed, no less than five structures lie superficial to it. These 

 are (enumerating them in order from the vessel to the 

 surface) (i) the origin of the posterior belly of the digastric 

 muscle; (2) the mastoid process ; (3) the longissimus capitis; 

 (4) the splenius capitis ; and (5) the sterno-mastoid. 1 As 

 the artery runs backwards, it very soon emerges from under 

 cover of the first three of the structures mentioned, and a 

 little farther on it leaves the shelter of the splenius, and is 

 then covered by the sterno-mastoid alone. Issuing from 



1 It is not uncommon to find the artery between the splenius and the 

 longissimus capitis, as in Fig. 20. 

 VOL. Ill 5 



