66 ABNORMAL CONDITIONS OF THE AXIS. 



opened out by the pressure of the tumour. The tumour consists 

 of the membrana reuniens superior, skin, connective tissue, and 

 the substance of the cord spread out into a cyst, and almost 

 converted into fibrous tissue by hypertrophy of its connective 

 elements. Sometimes the tumour becomes pedunculated by 

 pressure, which the perfect laminae above and below exert upon it 

 during its rapid increase. It is common in the lumbo-sacral 

 region, but extremely rare in the back and neck, except when ac- 

 companied by internal hydrocephalus and considerable malforma- 

 tion of the skull. In the latter case the occipital bone exhibits 

 considerable deficiency. When dropsy occurs at a later period of 

 development, it gives rise to the formation of an enormous cyst 

 on the occiput or vertex, epicephalocele ; and when it occurs to- 

 wards the close of intra-uterine life it produces distention of the 

 skull and great enlargement of its neural arch, hydrocephalus. 



a. Spina bifida. 



265. A portion of the lumbar and sacral region of a new-born 



Child affected with spina bifida. The surface of the 

 tumour is ulcerated. From Sir A. Cooper's Museum. 



266. A vertical section of the lower part of the back and sacrum 



of a new-born Child with spina bifida. In this specimen 

 the chorda equina is incorporated with the walls of the 

 tumour. From Sir A. Cooper's Museum. 



267. A similar specimen with the spinal canal opened from 



behind. Hunterian. 



268. A vertical section of the lumbar and sacral region of a 



Child affected with spina bifida. The lower extremity 

 of the cord is incorporated with the walls of the tumour, 

 from which the lumbar nerves appear to arise. This pre- 

 paration and the last, No. 267, were taken from children 

 born of the same parents. Hunterian. 



269. A sacral spina bifida opened from behind; the sacral nerves 



have been cut through at their junction with the wall of 

 the cyst. 



270. The lumbar vertebrae and sacrum of a new-born Child 



with spina bifida, showing the defective condition of the 

 neural arches. Hunterian. 



271. A dried preparation, consisting of the bones and ligaments 



