Merorachischisis is a partial defect in vertebrae in which there exists no hernial protrusion. Though this condition is also known as spina bifida occulta, the latter term is perhaps more applicable to the defect which is accompanied by a small or an invisible hernia. The deficiency may occur in auy part of the bone and in any region of the spine. In the literature consulted, I find that it is most common in the lumbar region, less so in the sacral and least of all in the cervical. I have not been able to find an authentic case of it in the middle dorsal vertebrae. The statistics on spina bifida with tumor are, that it occurs once in a thousand births (one in eight hundred — J. D. Bryant). The frequency is probably greater for spina bifida occulta.
The influences which interfere with normal development of the vertebrae unquestionably operate