536 THE THORAX AND VERTEBRAL COLUMN 



time of the closure of the primitive neural groove. In a limited 

 area the edges of the groove fail to unite and the central canal 

 of the spinal medulla opens on the dorsal surface of the foetus. 

 The exposed area, which is elliptical in shape and brownish in 

 colour (the " area medullo-vasculosa " of Recklinghausen), 

 consists of a flattened zone of neuroglia containing a few nerve- 

 cells. Rudimentary anterior and posterior nerve -roots are 

 attached to the ventral surface of the undeveloped part of the 

 spinal medulla. Complete paralysis is present on both sides of 

 the body below the level of the anomaly. As the central canal 

 of the spinal medulla opens on the surface (Fig. 164, /), 

 septic infection rapidly occurs and death results shortly after 

 birth. These cases are therefore unsuitable for treatment. 



In the other varieties described the sac may be exposed by 

 a longitudinal incision, which divides to surround the tumour. 

 When the tumour is situated in the sacral region, a transverse 

 incision may be employed in order to keep the wound as far as 

 possible from the anus. On the dorsal aspect of the tumour 

 the skin is extremely thin over an area of variable extent, and 

 this pellicle is enclosed by the incision. The skin is undercut 

 on each side and the wall of the sac is opened. The subsequent 

 treatment depends on the precise nature of the tumour. 



In simple meningocele, part of the sac is removed and the 

 edges are carefully approximated. In myelo-meningocele the 

 spinal medulla and nerve-roots are freed, if adherent to the 

 inside of the sac, and are then replaced within the vertebral 

 canal. Part of the sac is removed and the wound is closed in 

 two layers sac wall and skin. 



In order to prevent leakage of the cerebro-spinal fluid, the 

 cut edges of the sac wall are turned backwards and their inner 

 surfaces are carefully stitched to one another. In myelo-cysto- 

 meningocele, part of the sac may be ligatured and removed, but, 

 in this case also, great care must be taken to prevent subsequent 

 leakage of cerebro-spinal fluid. 



Similar deformities occur in connection with the skull and 

 the membranes of the brain, but they are much rarer. Cranial 

 meningocele, encephalocele, and hydr-encephalocele correspond 

 respectively to spinal meningocele, myelo-meningocele, and 

 myelo-cysto-meningocele. They are usually found in the 

 median plane, and their commonest site is below the external 

 occipital protuberance in the occipital region. 



A hydr-encephalocele in the occipital region contains the 



