440 THE EXPERIMENTAL PRODUCTION OF AN INTERNAL HYDROCEPHALUS. 



as judged by the imperfect activity of the animal, should persist. In such a thinned 

 cortex it is quite difficult to distinguish between the gray and white matter. It 

 seems, on gross appearance, that the remaining portion of the brain tissue is com- 

 posed largely of fibers and that the nerve cells are spread out and condensed into 

 a very narrow zone beneath the pia, rendering macroscopic identification difficult 

 in the formalinized preparation. 



In practically all of the more pronounced hydrocephalics the basal ganglia 

 may be made out on examination of the inferior surface of the ventricles from above. 

 The same picture of prominent masses of the ganglia is shown on coronal section, 

 but the best views are afforded in the specimens in which the top of the cranium 

 has been removed by a transverse cut. The general appearance of these masses 

 is given in figure 16, from a kitten which was sacrificed 22 days after a subarachnoid 

 injection of 1 c.c. of a 10 per cent suspension of lampblack. On each side two 

 rounded masses project into the enormously dilated ventricles; these represent the 

 more or less undisturbed nucleus caudatus and nucleus lentiformis. The thalamus 

 is obscured somewhat in a gentle swelling in the medial portion of each hemisphere. 

 The dislocation of these nuclear masses is not marked, for they are an integral part 

 of the brain tissue in approximation to the base of the skull ; changes here are much 

 less pronounced than in the vertex. Quite similar to this survival of the basal 

 ganglia is the isolation (on development of an internal hydrocephalus) of the fiber 

 bundles of the fornix, for these maintain a strand-like prolongation on the floor of 

 these dilated ventricles. Other fiber-bundles likewise can be made out, dislocated 

 to a greater or lesser extent in the enlargement of the third and lateral ventricles. 

 Such a pushing-back holds for the fibers of the corpus callosum (fig. 20). 



There is no essential difference between the internal hydrocephalus produced 

 by intraventricular injection of lampblack and that produced by subarachnoid. 

 Record has been made of minor differences, such as the more or less extensive 

 obliteration of the third ventricle and of the septum pellucidum in the direct 

 intraventricular injections, as compared to the partial survival of these structures 

 in the subarachnoid type. Most marked of all the differentiations, however, is the 

 variation in the distribution of the carbon granules found at autopsy. In the 

 kitten receiving ventricular injection a dense black layer of granules obscuring the 

 picture is customarily found in the basal regions of the dilated cerebral ventricles 

 (fig. 10). In the upper half of the cavity, however, the amount of lampblack is 

 much less. Quite unlike this is the much smaller amount of carbon visible in the 

 dilated ventricles of kittens injected by the subarachnoid route. In these, collec- 

 tions of granules, scattered and small in amount, are the usual findings in the 

 ventricular floor (as in fig. 16), but in some of the specimens the walls of the ven- 

 tricles are obscured by a deposit giving in the gross a brownish tint. 



An interesting feature of the partial obliteration of the basal markings by the 

 dense layer of carbon granules in such intraventricular injections concerns the rela- 

 tions of the choroid plexus. This appears, in the formalin specimen, as a delicate 

 filament in each ventricle, only slightly obscured by the lampblack. These plexuses 

 in some specimens remain fairly free from such carbon deposition, probably due to 



