THE EXPERIMENTAL PRODUCTION OF AN INTERNAL HYDROCEPHALUS. 439 



some of the cases the third ventricle seems obliterated by its marked enlargement 

 and by the rearrangements of the walls of the interventricular foramina; in others 

 the form of this ventricle is still left, though the whole structure has greatly increased 

 in all of its dimensions (fig. 19). The underlying basal nuclei seem to survive this 

 experimental increase in cerebro-spinal pressure most efficiently; their markings 

 are still wholly visible in the basal view of the sectioned specimen (fig. 16). These 

 general characteristics hold for practically all the specimens obtained. The whole 

 process may be likened to a partial reversion to the embryonic type of cerebral 

 ventricle. 



The essential feature of this experimental lesion (the dilatation of the cerebral 

 ventricles) must be taken as the initial, direct result of the increased pressure of the 

 cerebro-spinal fluid; this pressure is, in its turn, to be referred to the obliteration 

 of certain of the pathways of the cerebro-spinal fluid and the consequent damming 

 back of the fluid. For, with the chief production of the fluid intra ventricular (by 

 choroid plexuses), and with the obstruction to flow distal to the third ventricle, 

 it seems but natural that the necessary readjustments should occur within the 

 lateral ventricles. The initial increase in the size of these ventricles is the direct 

 result of the increase in pressure, but the enormous dilatation (figs. 10, 14, and 16) 

 met with in kittens is due to the potential distensibility of the head. This permits 

 a tremendous increase in the size of the lateral ventricles, not possible under other 

 conditions; and associated with this relatively extreme dilatation of the ventricles 

 in kittens is the partial rounding-up of the different diverticula of the original 

 cavities. Thus, the body and anterior horn of each lateral ventricle is early con- 

 solidated into a general, undifferentiated fluid-container; the posterior prolonga- 

 tion is included at about the same time. The temporal cornu, running anteriorly 

 toward the temporal pole, soon after shows evidence of enlargement in consequence 

 of the increasing pressures, and then takes part in the general process of ventricular 

 dilatation. The more extreme the enlargement, the more the distinction between 

 the temporal prolongation and the main body of the lateral ventricles is eliminated. 

 The net result of these alterations is that, on either coronal or transverse sections, 

 the lateral ventricles, instead of appearing as mere slits as in the control or cinnabar 

 kittens (fig. 10), seem to occupy, with their content of cerebro-spinal fluid, the major 

 portion of the kitten's cranial cavity (figs. 10 and 20). 



The thinning of the cerebral cortex is as remarkable and as extreme as the 

 dilatation of the ventricles. Normally, the gray and white matter of the cortex 

 practically fills the cranial chamber, with the exception of the narrow slits of the 

 ventricles. This is shown in gross in the normal control animals in figures 10, 19, 

 and 20. In the kittens receiving either intraventricular or subarachnoid injections 

 of lampblack the cortex becomes, within 10 days, reduced to a thin sheet of nervous 

 tissue 1 to 4 mm. in thickness. For the most part the extreme reduction in thick- 

 ness is in the parietal and adjacent areas; around the temporal or frontal poles, 

 resting on the more or less fixed portion of the skull, the thinning out of cortex may 

 not be so extreme, though some cases show marked thinning of temporal cortex. 

 This reduction of cortex is striking, and it is remarkable that any cerebral function, 



