What are the causes of aerania? From some of its forms, it is clear that there has been hydrocephalus followed by disruption (Morgagni, Penada, Sandifort, Klein, Otto). In an embryo figured by 111. Schroeder Van der Kolk, the summit of the head is extended by hydrocephalus, and has on its superior surface a black gangrenous spot which seems to prognosticate a rupture.
In another foetus I observed a fissure in the midst of an analogous spot. According to my opinion, the lacerated bags, which are sometimes found on or in the summit of the naked internal surface of the basis cranii, or at the back part of the more developed skull, are caused by such ruptures. Tiedemann gives a description of such a bag, filled with serofts fluid, but not yet burst, and situated upon the head of a fmtus, which has the ex ternal appearance of acrania. (Fig. 612.) taneous malformation of the brain and of the skull. Why I do not impute these malforma tions to external injury, such as the leaping of a monkey on the belly of a pregnant woman (Sandifort), to a fall down stairs (Pauli), or to the influence of imagination, needs not be demonstrated.
III. Fissure of the Back Part of the Body.
Ilydrorachis and Spina bda.— Fissure of the spinal column (spina bifida), and dropsy of the spinal medulla, occur each separately, or connected together. In the highest degree of fissure, the vertebral bodies even are cleft (J. T. Meckel, Tulp, Fleischmann). Fig. 613. represents such a case, after Cruveilhier.
But in those cases in which the flat basis of the skull is only covered with a membrane and with cerebral nerves, in those in which there is a spongy substance upon it, and in those in which the skull, although flat, is otherwise complete, not the least probability exists of the rupture of a cerebral vesicle at an early period of formation. I am able to prove this, I think, by a small foetus of two months, in which the superior part of the skull is wanting, and in which a spongy mass occupies the place of the brain.
It shows that aerania may also be a pri mitive malformation, occasioned by the simul In a less degree, the vertebral bodies are complete, but their arcs very defective, being completely wanting, or laterally incurved and fused together. In the lowest degree, the two halves of the vertebral arcs are completed, but not united together, so that posteriorly an open space remains between them, and a fis sure occupies the place of the processus spinosi, which are separated into two lateral and equally incurved parts.
When this form of fissure of the spinal column is not accompanied by hydrorachis, both parts of the vertebral arcs are not bent laterally, but meet each other so ex actly, that no open space remains between them. Sometimes the fissure is extended over the whole vertebral column (spina bda totalis), sometimes it is but partially cleft (spina bifida partials). The partial fissure occurs more frequently in the lumbar than in the cervical region of the column. The cause of the greater frequency of the partial fissure in the lumbar region is to be im puted to the termination of the spinal me dulla in this region ; to its expansion there under the form of cauda equina ; to the larger sheath formed there by the dnra mater ; and to the very limited tendency which the osse ous nuclei of the lumbar and sacral vertebrae show to unite themselves into an arc, which therefore remains always open at the inferior part of the sacrum. Although it occurs some
times alone, this sort of fissure is generally accompanied with dropsy of the spinal medulla (hydrorachis), that is to say, with a sac of a red dish-violet colour, in which fluctuation is easily discerned. Its external covering is sometimes formed by the skin, and then it has the usual colour of the body ; the skin, however, does not in most cases cover the whole surface of the tumour, but ceases at its circumference, and the rest of its surface is only covered with the dura mater. When the child lives, the dura mater becomes, after some time, thicker, harder, and more solid. When the tumour is covered with the skin, the dura mater is to be found under it. These membranes become often so thick, and so intimately united to gether, that it is nearly impossible to separate them from each other. The serum contained in the tumour is of a very variable quality, principally composed of albumen, mucus, ge latin, and muriate of soda (Bostock). It is effused between the pia mater and the arach noidea, or between this and the dura mater, or in the primitive canal of the spinal me dulla. If this canal remains open, the hydro rachis is in general accompanied with hydro cephalus interims. Sometimes these sacs are found on more than one spot of the spinal medulla, or divided into two by a septum. The size of the sac varies, and the complication with hydrocephalus is very dangerous. If this is the case, the artificial opening of the sac has a very injurious effect. Convulsions and exu dative inflammation are in most of the cases excited by it. In some very rare cases the operation was attended with success. Sir Astley Cooper healed hydrorachis by reiterated puncturing with a thin needle and by com pression of the tumour. Dubourg is said to have treated it with success by means of ex cision of the tumour and bringing together the lips of the wound with needles, in the same man ner as in the operation for hare-lip. Beynard tied a ligature round the sac. E. de Thine court compressed the tumour, after having opened it, with two small rods, which he connected and pulled together by means of ribbons. The noxious effects of hydrorachis after the child's birth make it necessary to try an operation. Before birth this mal formation seems not to have the least in fluence upon the health of the child : it is well nourished and duly constituted. After birth the noxious effect is modified by the different seat of the tumour. When seated in the lumbar and sacral region, it is the least dangerous. It is known that some indi viduals have lived with it twenty-eight years. In most cases, however, paralysis of the in ferior part of the body is its consequence. Hydrorachis in the cervical region is much more dangerous. One case of this is men tioned in my " Tabula?," in which death sud: denly occurred on opening the tumour.