THE BACK. 1443 



TABLE INDICATING THE LEVEL OF THE MORE IMPORTANT STRUCTURES IN 



RELATION TO THE SPINES OF THE VERTEBRAE Continued. 



Spines of Vertebrae. Origins of Spinal Nerves. 



Level of other Structures. 



1 Lumbar . 4 and 5 Sacral 



-Conus medullaris. 



Lower limit of pleura (mid-axillary line). 



Hila of kidneys. 



Head of pancreas. 



Right flexure of colon. 



Portal vein. 



Descending part of duodenum. 



Greater curvature of stomach. 

 ^Bile-duct. 



f Commencement of ureters. 

 \ Lowest part of head of pancreas. 

 ? Inferior limit of spinal medulla in child. 

 -! Inferior ends of kidneys. 

 (Horizontal part of duodenum. 

 l Highest part of crest of ilium. 



4 . A Bifurcation of aorta. 



( Umbilicus. 

 ( Common iliac arteries. 

 ' \Valveofthecolon. 



1 Sacral Sacral promontory. 



2 . ... . . . . Lower end of sub-dural space. 



f Superior end of gluteal cleft. 



3 . j-j Inferior limit of sub-arachnoid and sub- 



j I dural spaces. 



Spinal Medulla. The spinal medulla ends opposite the inferior border of the 

 first lumbar spine ; in the infant it reaches to the interval between the second and 

 third lumbar spines. The cervical enlargement, which corresponds to the lower four 

 cervical and the first two thoracic segments, ends opposite the seventh cervical 

 spine. The lumbar enlargement lies opposite the last three thoracic spines. The 

 five lumbar segments are opposite the ninth, tenth, and eleventh thoracic spines, 

 while the five sacral segments extend from the lower border of the eleventh 

 thoracic to the lower border of the first lumbar spine. 



The sub-dural space extends down to the level of the second sacral spine. In 

 performing the operation of lumbar puncture (Quincke) a fine trochar and cannula 

 are introduced into the sub-arachnoid space below the level of the spinal medulla, 

 the puncture being made \ to J in. to one side of the interspinous ligament in the 

 interval between the third and fourth or fourth and fifth lumbar spines. The 

 instrument should be directed medially towards the median plane and very slightly 

 upwards. In the adult the distance of the dura mater from the surface is about 

 2 in., in the infant f in. 



Fracture-dislocations of the vertebral column are commonest in the lower cervical 

 and thoracico-lumbar regions ; that is to say, where the movable cervical and lumbar 

 regions join the more fixed thoracic region. The vertebral column above the 

 injury is generally displaced forwards, so that the spinal medulla is often severely 

 lacerated or completely torn across by the superior end of the portion of the column 

 below the fracture. It is important to remember that in consequence of the short- 

 ness of the spinal medulla as compared with the vertebral column, the origins of 

 the spinal nerves are at a higher level than their exits from the vertebral canal. 

 The distance between origins from the spinal medulla and exits through the 

 intervertebral foramina becomes greater the further down the nerves are, the 

 lowest nerve trunks running almost vertically downwards. The cervical nerves 

 leave the vertebral canal above the vertebrae after which they are named (except 

 the eighth, which is above the first thoracic vertebra) ; the thoracic, lumbar, and 

 sacral nerves, on the other hand, leave the canal below the correspondingly named 

 vertebrae. 



92 a 



