536 



DISSECTION OF THE BACK. 



attach- 

 ments. 



Interspinal 

 muscles : 



in neck ; 



in dorsal 

 region : 



in loins ; 



their use. 



Inter- 

 transverse 

 muscles : 



in neck ; 



in dorsal 

 region ; 



in loins ; 



their use. 



Dissection 

 of sacral 

 nerves. 



Five sacral 

 nerves. 



are separated by fine areolar tissue. Each arises from the upper 

 and back part of a transverse process, and is inserted into the 

 lower border of the neural arch of the vertebra next above. The 

 first springs from the transverse process of the second vertebra. 



The INTERSPINALES are arranged in pairs in the intervals 

 between the spinous processes. They are most developed in 

 the neck and loins. 



In the cervical region they are small rounded bundles 

 attached to the bifurcated extremities of the spines from the 

 axis downwards. 



In the dorsal region iriterspinal muscles are only present in one 

 or two of the highest and lowest spaces. 



In the lumbar region they are thin flat muscles, reaching the 

 whole length of the spine, one on each side of the interspinous 

 ligament. 



Action. The muscles help to extend the spine. 



The INTERTRANSVERSALES lie between the transverse processes 

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

 dissected. 



In the neck they are double, and resemble the interspinal muscles 

 of the cervical vertebrae. 



In the dorsal region they are single rounded bundles of small 

 size, and are found only between the four or five lower vertebrae. 

 They are represented in the middle spaces by thin fibrous bands. 

 which constitute the so-called intertransverse ligaments. 



In the lumbar region there are two muscles in each space. The 

 outer set are thin flat muscles between the transverse processes. 

 The inner muscles are rounded bundles in a line with those of the 

 dorsal region ; they are attached to the accessory processes above, 

 and the mamillary processes below ; and the highest is between the 

 last dorsal and the first lumbar vertebrae. 



Action. The intertransverse muscles assist in bending the spine 

 laterally. 



Dissection (fig. 193, p. 537). To see the posterior divisions of 

 the sacral nerves, it will be necessary to remove the part of the 

 multifidus spinae covering the sacrum. The upper three nerves are 

 each split into two ; their external branches will be found readily 

 on the great sacro-sciatic ligament, from which they may be 

 traced inwards ; the inner branches are very slender and difficult 

 to find. 



The lower two nerves are very small, and do not divide like 

 the others. They are to be sought on the back of the sacrum, 

 below the attachment of the multifidus spinae. The fourth comes 

 through a sacral aperture, and the fifth between the sacrum and 

 coccyx. The coccygeal nerve is still lower, by the side of the 

 coccyx. 



SACRAL NERVES (fig. 193). The posterior primary branches of 

 the sacral nerves are five in number. Four issue from the spinal 

 canal by the apertures in the back of the sacrum, and the fifth 

 between the sacrum and the coccyx. The first three have the 



