MULTIFIDUS SPIN3. 371 



pair of bones would be scarcely appreciable, as in the case of the inter- 

 spinales. 



Dissection. The multifidus spinae muscle, which fills the hollow by the 

 side of the spinous processes, may be now dissected. The upper part of 

 the muscle is to be prepared and learnt by the dissector of the head and 

 neck. It will be laid bare by cutting through the insertion of the semi- 

 spinalis, and everting this. 



* Over the sacrum the thick aponeurosis covering the multifidus and the 

 erector spinre must be turned aside. In the dorsal region the muscle will 

 appear on detaching, and drawing the semispinalis from the spines. 



* The MULTIFIDUS SPINAE muscle extends from the sacrum to the second 

 vertebra, and is much larger towards the pelvis than in the neck. 



On the back of the sacrum it takes origin between the central and ex- 

 ternal row of processes, as low as the fourth aperture ; from the inner 

 surface of the iliac spine (posterior superior) of the hip bone ; and from 

 the ligaments connecting this bone to the sacrum. It is attached differ- 

 ently along its outer edge (origin) in the several regions of the spine : 

 In the loins it arises by large fasciculi from the accessory and the articular 

 processes. In the dorsal region, from the transverse processes. And in 

 the neck, from the articular processes of the five lower vertebrae. From 

 these attachments the fibres are directed obliquely inwards, some extend- 

 ing more than the length of one vertebra to be inserted into the spines 

 and the neural arches of the vertebra? from the second cervical to the third 

 sacral. 



This muscle fills chiefly the vertebral groove, and is concealed by the 

 erector spinae and the semispinalis. The internal branches of the vessels 

 and nerves in the back lie along its outer border. The small muscles de- 

 scribed below may be said to be parts of the multifidus. 



Action. By the use of the muscle of both sides, the spinal column can 

 be extended ; and by the contraction of one, the spine will be rotated in 

 the dorsal region and the neck, the face being turned to the opposite side. 



* Rotatores dorsi (Theile). These are eleven small muscles beneath the 

 multifidus spinae in the dorsal region, and are separated from that muscle 

 by fine areolar tissue. Each is attached inferiorly to the tip and upper 

 edge of a transverse process, and superiorly to the lower border of the 

 neural arch of the vertebra next above. The first springs from the trans- 

 verse process of the second vertebra. 



Action. These small rotators will assist the larger muscle (multifidus) 

 in turning the trunk to the opposite side. 



* The aponeurosis common to the multifidus and erector spinre is fixed 

 firmly to the surrounding bones, and furnishes attachment to the muscu- 

 lar fibres. In the middle line it is united with the spines of the lower 

 lumbar vertebrae and sacrum. On the outer side it is attached to the pos- 

 terior part of the iliac crest, and to the outer row of tubercles on the back 

 of the sacrum, being connected at the last spot with the great sacro-sciatic 

 ligament. Above, it is continued some way on the surface of the erector 

 spinae, but further on the longissimus dorsi than the ilio-costalis. Below, 

 the latissimus dorsi and the vertebral aponeurosis blend with its cutaneous 

 surface (p. 360). 



* Dissection (fig. 120). To find the branches of the sacral nerves, it 

 will be necessary to remove the part of the multifidus spinae which covers 

 the sacrum. The first three are split into two eacli : their external pieces 

 will be found readily on the great sacro-sciatic ligament, from which they 



