362 DISSECTION OF THE BACK. 



the sacro-lumbalis may be turned outwards, so as to uncover the fleshy 

 slips of its accessory muscle, which are fixed to the angles of the ribs : a 

 muscular slip (cervicalis ascendens) is prolonged from this to the neck. 



* In preparing the sacro-lumbalis muscle, the external pieces of the dor- 

 sal nerves with their accompanying arteries will appear. 



* Before the longissimus can be displayed, it will be needful to detach, 

 and raise towards the spinous processes the thin muscular fasciculus of the 

 spinalis dorsi, which lies between that muscle and the spines of the verte- 

 brae in the dorsal region. Then the attachments of the longissimus dorsi 

 are to be traced out. Externally it has thin muscular processes of insertion 

 into about the eight lower ribs. Internally it is inserted into the trans- 

 verse processes of the lumbar and dorsal vertebrae by rounded tendons ; 

 and for the purpose of seeing these tendons, the longissimus should be 

 drawn away from the spinous processes, and its superficial aponeurosis 

 should be cut through belovv the ribs, along the line of separation between 

 the muscle and the fleshy multifidus spinae on the inner side. From this 

 muscle, as from the sacro-lumbalis, a fleshy piece (transversalis colli and 

 trachelo-mastoid) is continued into the neck. 



* Between the longissimus and the multifidus spinae are the internal 

 pieces of the dorsal and lumbar nerves, and of the intercostal and lumbar 

 arteries and veins. 



* The SPIXALIS DORSI is placed on the side of the spines of the dorsal 

 vertebrae, and is united with the longissimus dorsi. Interiorly it arises by 

 tendinous processes from the spines of the last two dorsal and first two 

 lumbar vertebrae, and by fleshy fibres from the contiguous tendon of the 

 longissimus. From this origin the fibres ascend, forming arches, whose 

 concavity looks inwards, and are connected by tendinous processes to the 

 spines of the dorsal vertebrae as low as the eighth or ninth, or only for half 

 that extent. 



Action. Both muscles contracting will extend the dorsal region of the 

 spine. Perhaps the muscle of one side may tend to incline the spine 

 laterally. 



* The ERECTOR SPIX^E is the muscular mass on the side of the spine in 

 the lumbar region. It is single and pointed below ; and its cutaneous sur- 

 face is covered near the sacrum by a wide and strong tendon, which is 

 common to it and the multifidus spinae. The muscle arises at the pelvis 

 from the posterior fifth of the crest of the hip-bone at the inner aspect, 

 except opposite the upper spinous process: in the lumbar region it is at- 

 tached by fleshy and tendinous pieces to the transverse processes, to the 

 tubercle (process, accessorius) at the root, and to the layer of the fascia 

 lumborum external to each. Opposite the last rib it divides into ilio-cos- 

 talis and longissimus dorsi. 



* The ILIO-COSTALLS (SACRO-LUMBALIS) is the smallest of the two 

 pieces resulting from the division of the erector spinae. Its fibres end in 

 six or seven flat tendons, which are connected together by their margins, 

 and are inserted into the angles of as many of the lower ribs. The muscle 

 is continued onwards to the other ribs and the neck by a fleshy part, which 

 constitutes the two under-mentioned muscles: 



* The mitsrnlus accessorius ad sacro-lunibalum begins by a series of 

 tendinous and fleshy bundles on the angles of the lower six ribs, internal 

 to the insertion of the ilio-costalis ; and it ends in tendons, which are in- 

 serted into the remaining ribs (upper six), in a line with the ilio-costalis, 

 and into the posterior transverse process of the seventh cervical vertebra. 



