THE DISSECTION OF THE BACK 177 



multifidus pass over two, three, or four vertebrae, and are inserted into the 

 whole length of the various spinous processes of the movable vertebrae as 

 high up as the epistropheus (O.T. axis). 



Musculi Rotate-res. These are a series of small muscles which may be 

 exposed by raising the multifidus. In the dorsal region each muscle springs 

 from the root of a transverse process, and is inserted into the lamina of the 

 vertebra immediately above, close to the root of the spinous process. 

 Somewhat similar muscles have been described in the cervical and lumbar 

 regions, and also a series of longer and more superficial slips which connect 

 alternate vertebrae with each other. 



Musculi Interspinales and Intertransversarii. The interspinous 

 muscles can hardly be said to exist in the dorsal region, except in its upper 

 and lower parts, where they are present in a rudimentary condition. In 

 the neck they are arranged in pairs, occupying each interspinous interval, 

 with the exception of that between the epistropheus and atlas. In the 

 lumbar region also they are well marked and in pairs : here they are 

 attached to the whole length of the spinous processes. The intertransverse 

 muscles are strongly developed in the lumbar region, and occupy the entire 

 length of the intertransverse intervals. Additional rounded fasciculi may 

 be observed passing between the accessory processes. These are termed 

 the interaccessorii. In the dorsal region intertransverse muscles poorly 

 developed are found only in the lower three or four spaces. In the cervical 

 region they are present in pairs and will be examined subsequently. 



Levatores Costarum. These constitute a series of twelve 

 fan-shaped muscles, which are classified as muscles of the thorax, 

 but they are exposed when the longissimus and ilio-costalis 

 are removed, and therefore should be examined now. They 

 pass from the transverse processes to the ribs. The first 

 muscle of the series springs from the tip of the transverse 

 process of the last cervical vertebra, and, expanding as 

 it proceeds downwards and laterally, it is inserted into the 

 outer border of the first rib, immediately beyond the 

 tubercle. Each of the succeeding muscles takes origin from 

 the tip of a thoracic transverse process, and is inserted into 

 the outer surface of the rib immediately below, along a line 

 extending from the tubercle to the angle. 



Posterior Branches of the Sacral Nerves. These are 

 very small. The upper four will be found emerging from 

 the posterior sacral foramina ; the fifth appears at the lower 

 end of the sacral canal. 



To expose the upper three the multifidus covering the 

 upper three sacral apertures must be carefully removed. 

 Each of these three nerves will be found to divide in 

 the usual manner into a medial and lateral division. 



The medial divisions are very fine, and end in the 

 multifidus. 



The lateral divisions are somewhat larger, and join 



VOL. II 12 



