378 SURGICAL APPLIED <4Avtr0JifX.cChap.xvm. 



genital malfoi'mations of tlie vertebral canal associated 

 with the protrusion of some of its contents in the 

 form of a fluid tumour. The malformation usually 

 consists in an absence of the neural arches and spines 

 of certain of the vertebrae, and the tumour therefore 

 projects posteriorly. Spina bifida is most common in 

 the lumbo sacral region, the neural arches of the last 

 lumbar and of all the sacral vertebrae being absent. 

 Next in frequency it is found limited to the sacral 

 region. It is rare elsewhere. (1) The membranes 

 may protrude alone (spinal meningocele). (2) The 

 membranes may protrude together with the spinal 

 cord and its nerves (meningo-myelocele). (3) The 

 membranes may protrude with the cord, the central 

 canal of which is dilated, so as to form a sac cavity 

 (syringo-myelocele). 



The meningo-myelocele is the most common form. 

 The first-named variety is rare, the last-named very rare. 

 When the cord occupies the sac it usually adheres to 

 its posterior wall, the nerves running transversely 

 across the sac to reach the intervertebral foramina. 



As may be expected, spina bifida is very commonly 

 associated with some evidence of injury to the nerves 

 arising from the lower part of the spinal cord. In the 

 majority of instances certain of these nerves would 

 appear to have become atrophied through pressure. 

 In some cases the nerve affection takes the form of club- 

 foot of a severe grade. In other instances there is 

 more or less complete paralysis of the lower limbs, 

 bladder, and rectum. 



" The anatomy of spina bifida assumes a primary 

 defect of development of the mesoblast, from which 

 the structures closing in the vertebral furrow are de- 

 veloped. After the closure of the neural furrow it 

 would appear that the processes of mesoblast, which 

 subsequently insinuate themselves between the primi- 

 tive spinal cord and its overlying epiblast, ai'e formed 



