THE BACK. 



31 



Colon. The ascending and descending portions of the colon pass vertically 

 along the outermost part of the right and left kidneys respectively ; the part of the 



Fig. 15. DIAGRAM SHOWING THE VARYING RELATIONS OP THE ROOT- ""--^I" 



ORIGINS OF THE SPINAL NERVES TO THE SPINES OF THE VERTEBRA. fRj " CERV ' CAt 



(After R. W. Reid.) 4 C E *V,CA J U i 



intestine which is in contact with the abdominal wall is 

 placed immediately internal to a line carried vertically up- 

 wards from the central point of the iliac crest. 



The pancreas crosses the spinal column opposite the 

 twelfth dorsal and first lumbar spines, and the third part 

 of the duodenum from the second to the third lumbar 

 spine. 



Spinal cord and origins of spinal nerves. The 

 lower end of the spinal cord in the adult corresponds 

 generally to the interspace .between the first and second 

 lumbar spines, and is not subject to much variation in 

 level ; but in the infant it reaches to the third lumbar 

 spine. The cervical enlargement extends downwards to 

 about the seventh cervical spine, and the lumbar enlarge- 

 ment corresponds mainly to the last three dorsal spines. 



The relations of the origins of the spinal nerve-roots to 

 the spinous processes of the vertebrse vary to some extent 

 in different individuals, especially in the thoracic region, 

 the range of any given dorsal nerve-root being about equal 

 to the distance between three adjoining spines, or two 

 interspinous intervals, as is shown in the accompanying 

 diagram (fig. 15) constructed from the observations of 

 R. W. Reid upon six subjects. The following rules will, 

 however, serve to indicate with sufficient accuracy the 

 average position of the several nerve-roots : The second 

 cervical nerve arises opposite the neural arch of the atlas, 

 the third opposite the spine of the axis, and the fourth 

 opposite the interval between the second and third cervical 

 spines. The lower four cervical nerves arise each opposite 

 the spine of the second vertebra above the place of exit of 

 the nerve from the spinal canal. The origins of the upper 

 six dorsal nerves are about on a level with the spines of 

 the third, and of the lower six with the spines of the 

 fourth vertebra above their respective places of exit. The 

 lumbar nerves arise in the neighbourhood of the tenth 

 and eleventh dorsal spines, and the sacral nerves between 

 the eleventh dorsal and first lumbar spines. 



I2 T H DORSAL' 



