Deficiencies of development involve, as has been stated, various anomalies in the shape of the several vertebrae, and also, as will further appear, deformities of the whole column. Moreover the approximation to each other in form, which the vertebrae exhibit at the limits of the natural divisions of the column, sometimes gives the appearance of a vertebra being deficient. In this manner the last dorsal assumes much of the character of a lumbar vertebra, and more frequently the last lumbar becomes a sacral bone: this transference from the lumbar to the sacral region may be symmetrical, and occur on both sides, or may take place on one side only. On the contrary the first lumbar may approach a dorsal vertebra in character, and sometimes it bears the rudiment of a thirteenth rib: or the first sacral vertebra may resemble the last lumbar. Finally, the vertebrae are subject to manifold deformities at different periods of life, in consequence of exostosis, osteophyte, and partial absorption of the cicatrization which succeeds the loss of substance occasioned by caries and necrosis, etc.

Some of the deformities of the vertebral column are congenital; others, and those the greater number, come on at different ages after birth, and consist of various forms of curvature of the column. Those of the former class are for the most part occasioned by so serious affections of the central organs of the nervous system (hydrorachis combined with anencephalus, encephalocele, &c), that they very rarely come under observation at the later periods of life. The deformities produced by high degrees of fission of the vertebral column, and the curvatures which accompany them, are instances of this kind. In other cases the curvature of the spine, and the other deformities coexisting with it, are produced by the contraction of muscles, to which certain diseases of the nervous centres give rise. Sometimes the curvature results from deficiency of the lateral half of a vertebra, or from unequal development of the two halves of the column, or from the presence of one or more half-vertebrae too many. Lastly, fission of the thorax or abdomen, or eventration, may make the spinal column deviate from its natural direction. The form of the deviation may vary; it may be a simple curvature, or, as is the case with those which come on after birth, it may be a compound of two or more curves, etc.

I venture to introduce in this place the description of three cases of original deformity of the spinal column: they are of rare occurrence, and the first of them is perhaps unique.1