Spin a Bifida 205 



It is possibly caused by an increase in the amount of cerebro-spinal, 

 subarachnoid fluid in the early development, whereby the coalescence 

 is prevented. The tumour is in the exact median line and has a firm 

 attachment. It is often associated with imperfect innervation of the 

 pelvic viscera, and with arrested development of the lower extremities. 



When the child screams, some of the cerebral fluid is displaced 

 from the interior of the skull and into the spinal canal, the tumour 

 becoming more tense ; and by gentle compression of the tumour 

 some of the fluid can be squeezed into the cerebro-spinal canal, with 

 the effect of causing irregular muscular movements or even convul- 

 sions. 



Sometimes the sac contains no nerve cords or branches ; some- 

 times the nerves are spread over its inner surface. The sac may be 

 lined by the substance of the cord itself, the serous fluid being con- 

 tained in the immensely dilated central canal of the cord. This is 

 likely to be associated with internal hydrocephalus (p. 56). If the cord 

 or the large nerves of the cauda equina be in the sac, they occupy the 

 median part. 



Operative treatment is directed towards obliterating the communi- 

 cation with the interior of the spinal canal, and the more slender the 

 communication the greater the prospect of cure. 



To put a ligature round the base of the tumour may be to set up a 

 meningitis spreading from the cord to the brain ; to tap and empty 

 the sac is to leave the brain high and dry, with no counterpoise to the 

 cerebral circulation ; and freely to inject a stimulating fluid may be 

 to excite meningitis and encephalitis, the child dying in convulsions. 



The spinous processes of the upper cervical vertebras can just be 

 made out at the nape of the neck, especially that of the axis ; the spines 

 of the sixth and seventh are long, horizontal, and conspicuous. Indeed, 

 the spine of the seventh (vertebra promi?iens] sometimes juts out so 

 conspicuously as to suggest the appearance of angular curvature. 



The dorsal spines are long, and overlap one another so as to pre- 

 vent extension in the chest region, otherwise the heart and lungs might 

 be interfered with in their work. The tip of a dorsal spinous process 

 descends well over the body of the vertebra below. The lumbar spines 

 are large and horizontal, and well hidden between the large masses 

 of the erector spinae. 



In counting the spinous processes the seventh cervical is at once 

 recognised, with the sixth close above it, and the first dorsal just below. 

 The third dorsal spine corresponds with the root of the spine of the 

 scapula, and the fourth lumbar spine is on the level of the top of the 

 iliac crests. 



In the cervical region the spinal cord may be readily injured by a 

 stab, but in the dorsal and lumbar regions it is well protected by the 

 imbricated laminae. 



The transverse process of the atlas stands well out in the side of 



