1. Deficiency And Excess Of Development

Deficiency of the whole vertebral column is met with only in monsters which are very incompletely developed; more commonly, only a portion of it is wanting. The latter deficiency occurs in cases of acephalus, and corresponds in extent with that of the concurrent defect in the neck or trunk. An allied but less deficiency, in which one or more vertebrae or half vertebrae are of small size, or altogether absent, sometimes co-exists with other malformations of the skull and vertebral column, with hemicephalus in the cervical portion of the spine, and with spina bifida: sometimes it is unaccompanied by any anomaly of the kind, occurring in persons who are otherwise naturally formed. In well-formed persons a cervical vertebra is sometimes, but very rarely, wanting; a similar deficiency in the dorsal or lumbar region is less unfrequent. Moreover, the absence of a dorsal vertebra is usually made up for by a supernumerary one in the loins, and the deficiency of a lumbar is supplied by an additional sacral vertebra. It is interesting to observe, in persons who are in no other way deformed, how the want of one half of a vertebra, in the same manner as a half too much, produces congenital lateral curvature.

A faulty and insufficient development of the spinal column may arise from an original fusion of the bodies of two or more vertebrae; this congenital anchylosis is sometimes associated with other malformations, especially with spina bifida and hemicephalus, but sometimes it occurs in persons who are otherwise well formed.

Fission Of The Vertebral Column, Spina Bifida (Hydrorachis)

Fission Of The Vertebral Column, Spina Bifida (Hydrorachis), is an anomaly of great importance belonging to this class. In its nature it resembles hemicephalus, with which it is very frequently combined. It presents several degrees, which are discernible on the skeleton of the vertebral column: sometimes it involves the whole, sometimes only parts of the spine; and its extent, when partial, varies greatly. In its least degree, the half arches are developed, and occupy their natural situation; but, as they have not united, an aperture or fissure remains in the proper seat of union, the length of which depends on the number of vertebrae involved. In a higher degree, the half arches are incompletely developed, more or less of their extremities being deficient, and thus the fissure has a greater transverse diameter than in the preceding degree: usually, also, a larger number of vertebrae is affected. In a condition allied to this, the half arches are fully developed, but stand off from each other to a considerable extent, and are so turned round to the side of the bodies of the vertebras, that the line of their direction becomes, at length, continuous with the posterior surface of the bodies: they are usually then flattened from before backward; and, as in the form already mentioned, are here and there united with one another. Although there is no actual deficiency of development, the fissure becomes very wide, and diminishes in depth. In a still higher degree, the fissure involves not the half arches alone, but also the bodies of the vertebrae; and, in the highest degree of all, one of the half arches may be wanting, and a part, or even the entire half, of one or of several of the bodies. Fission of the vertebral column in its whole length, or of its cervical portion, scarcely ever occurs, unless hemicephalus and hydrencephalocele exist also. The most common situation of spina bifida is the lower dorsal and lumbar region. Fission of the sacral vertebrae is more rare: sometimes it occurs in two places together, and then usually one fissure is in the neck, and combined with hemicephalus, while there is another in the lumbar or lower dorsal region.

Excess of development is exemplified in the presence of an unusual number of whole or half vertebrae. In the former case, there are sometimes thirteen dorsal, or six lumbar vertebrae; the vertebral column is, to a corresponding extent, longer than natural; and, connected with the supernumerary dorsal vertebra, there is an additional rib. An excess of one or more halves of vertebrae occasions a congenital lateral curvature, in the same manner as a deficiency of halves of vertebrae; and it constitutes a most remarkable instance of scoliosis, of which I shall treat more at large hereafter.