Besides hydrorachis, some other malforma tions of the spinal medulla are observed some times to accompany fissure of the spinal column: 1. Complete want of the spinal medulla, com monly connected with acrania ; 2. Its appear ance under a cylindrical form,' with persistance of the primitive medullary canal (Morgagni, Santorini), which is sometimes double (Gall, Von Ammon) ; 3. Fissure of the spinal me dulla into two juxtaposed cords; so that it seems to be double, which is occasioned by an arrest of developement at that period of its evolution in which the two halves, of which it is formed, are as yet separate ; 4. The pre sence of a simple nervous expansion instead of spinal medulla ; 5. The lamellar form of the medulla ; 6. A too great length.
By all this it is proved, that fissure of the spinal column may be accompanied with hydrorachis, and with an imperfect deve lopement of the medulla. They are totally independent of each other, and each is pro duced by its own cause. It is, however, not very improbable that a voluminous sac on the medulla may prevent the union of the points of ossification, by which the vertebral arcs are to be formed ; but we are not, I think, justified in concluding from this that hydro rachis is the cause of the fissure of the vertebral column. For it may exist without fissure of the spinal column, if it has not acquired the form of a bag ; and the spinal column may be cleft although the spinal me dulla is intact. This leads me to the con clusion, that malformation of the spinal me dulla, hydrorachis, and fissured spinal column, do not essentially go together.
IV. Hydrocephalus congenitus.
Congenital dropsy of the brain. —Under this name we understand such a great volume of the head in a full-grown foetus that it opposes in general a mechanical impediment to partu rition, which can only be removed by an arti ficial diminution of the volume of the head. Its forms are —1. Hydrocephalus internus ; 2. Hydrocephalus externus.
1. Hydrocephalus internus is said to exist when the abnormal serous secretion occurs in the ventricles of the brain, wherefore it has also acquired the very rational name of hydrops ventriculorunz cerebri. It may be an altogether primitive malformation, when the brain is arrested at that period of its de velopement in which it has the form of a very thin vesicle, filled with a serous fluid. I have observed this condition principally in Cyclopes, and give an example of it in fig. 614.
In such case there is no indication of the hemispheres, nor of the convolutions of the brain, and, in general, no difference to be seen between the white and the grey cerebral substance. In small fcetuses of two months, in which the bones of the skull could not yet be discerned, this form of hydrocephalus has Internal hydrocephalus is, however, not always occasioned by arrest of develope ment in an early period of formation, but may be produced by chronic inflammation, (G. Vrolik), to which the child is, without
doubt, as much subject during uterine life as after its birth. The principal causes of it seem to be external injuries suffered by the pregnant woman, and sometimes even rated contact by the act of copulation, if the pelvis is large, and the womb seated very low. Pseudo-membranes are on this ac count often found on the internal surface of the expanded ventricles (G. Vrolik), by which the deposition of the serous liquor may be limited to one or more of the cerebral ven tricles, so as to produce an a-symmetrical expansion of the head ; this is, on the con trary, symmetrical, if both the lateral with the third and fourth ventricle are equally and universally extended by the fluid. The head acquires, in such case, an enormous, but sym metrical, volume (E. Sandifort, W. Vrolik). The slower such a secretion of fluid takes place, the slower the head increases in volume, and the less it endangers life, and the less the free evolution of the mental faculties is interfered with. Some cases are men tioned, in which life lasted sixty years (G. Vrolik), thirty years (Michaelis), and fifty four years (Gall). It is remarkable that in many of these cases, neither the senses nor the intellectual faculties were in the least im paired. This proves that the substance of the brain is not altered by it, and that the form only of the brain is changed by the unfolding of its convolutions. This unfolding is the consequence of the pressure which the fluid exercises from the inside towards the outside, and of the thereby augmented volume of the ventricles (Hunauld, Gall). Those who presume that through the influ ence of the serum exudated in the ven tricles the dissolution and even the total de struction of the cerebral substance may be effected, go evidently too far (Cruveilhier). However large may be the surface into which the hemispheres of the brain have been un folded, the white medullary substance can always be distinguished from the grey (G. Vrolik). The parts contained in the, ventricles are sometimes intact (G. Vrolik), but sometimes incompletely developed, and what we should call depressed (Aurivillius, Biittner, Malacarne, Klein). The corpus callosum assumes a thin lamellar form; the septum pellucidum and the fornix become thinner ; the glandula pituitaria and pinealis deviate in general from their natural condition (Friend, Malacarne, Wrisherg). The cerebral nerves are in general not changed, and the cerebellum is in most cases natural. The lumen of the cerebral arteries is commonly very large (Biittner), and Friend saw two in ternal carotids passing through the carotid canal of the right side. In a few cases there was observed a degeneration of the cerebral substance, which resulted in a deranged and feeble state of the mental faculties (Biittner).