CONGENITAL DISEASES OF THE YERVOITS SYSTEM 1. Acephalia, Amyelia.—The greatest disturbance of the central nervous system consists in the total absence of the brain and spinal cord. The vertebral column remains open posteriorly, the base of the skull is imperfectly developed, and there is complete absence of the calvarium. In amyelia the spinal ganglia and sensory roots are present and the latter exhibit an attempt to join the iinperfectly developed spinal marrow; muscles are also present, as well as those portions of the peripheral nerves which are derived from the spinal ganglia. Mon sters of this type are not viable and die in the frrtal period (cases of Manz, Leonowa, Petren, Gaile, etc.). Cases have also been observed with partially preserved spinal marrow (Wolfram).
2. Anencephalia (Hemicephalia). The term anencephalia themi ceplialia is not a good term on account of the analogous use of the prefix for unilateral disturbances of the cerebrum (Sternberg)] is used to de scribe a malformation in which the spinal marrow, the medulla oblon gata and portions of the basal ganglia are present, while the cerebral hemispheres are absent and tbe cerebellum is usually atrophic. There is no calvarium and the cranium is closed by a spongy, vascular mass which sometimes exhibits nodular swellings and prominences simulating cere bral convolutions (area cerebrovasculosa, Recklinghausen). Micro scopic examination of such cases has shown that the parts of the central nervous system which are present are, in the main, well developed, al though individual systems of fibres are absent or imperfectly formed (pyramidal tract, lateral cerebellar tract); while, on the other hand, cer tain nerve tracts, when the parts which they- are intended to supply are absent, may be abnormally developed and run in abnormal directions. The neurologic significance of these microscopic findings was recognized and elaborated by v. Monakow and his students. The peripheral nerve organs are developed even when their connections with the central organs are absent (autoclifferentiation, Roux).
It is possible that anencephalia is produced by cleft-formation in early Etta' life or by failure of the medullary tube to close; possibly the malformation is due to certain chemical abnormalities within the ovum. At all events, it has been possible by introducing chemical or
toxic substances into the ova of animals to prevent closure of the brain plate (Hertwig, Roux, Fere). Other forms of malformation of the cen tral nervous system have been produced in animals 1)3- mechanical means (Dareste, Tichomirow, Kol'mann). Several cases of anencephalia have been observed in the same family. The presence of anencephalia does not necessarily involve death of the fertits. It may be horn at the normal period and survive for several days. Sternberg and Latzko in their physiologic studies of an anencephalic monster which lived three days found that crying. sucking. defecation and urina tion, the corneal reflex, sensation of pain and discomfort, mimic reflexes, movements of Hie ex tremities and tendon reflexes in the arms and legs were present. Evidently these vi tal manifestations may yield valuable information in regard to the seat of reflex processes in the nervous system.
Anencephalia is often associated with other malformations affecting not only the spinal marrow (alterations in the central canal, etc.), but other organs also (aplasia of the adrenal bodies). There appears to be a preponderance of fenmles among anencephalic monsters.
3. Cyclopia (Cyclencephalia).—In this mal formation the brain canal is closed but the cerebrum exhibits marked alteration. The cerebral hemispheres are poorly developed and not separated from one another. The absence of symmetry in the nervous organs shows itself most markedly in the presence of a single eye in the median line, which is usually' very poorly developed. The cerebrum shows either cystic degeneration (icAgeli) or arrested development (Leonowa). The optic thalami and portions of the base of the brain sometimes exhibits a redu plication of the usual or normal etnbryonic structure. With cyclopia are occasionally combined malformations of the skeleton of the face (arrhincephalia, Kundrat), in which the nose may exhibit a variety of bizarre, snout-like deformities; children with this malformation are not viable (cases of Kundrat, Nageli, illonakow., Falk, Leonowa, etc.).