102 



TRANSITORY CAVITIES IN THE CORPUS STRIATUM. 



THE OCCURRENCE OF THE TWO STRIATE CAVITIES. 



In searching through the literature for illustrations of these cavities onty one could be 

 found which unquestionably had reproduced either of the spaces in the corpus striatum. 

 His (4, p. 124, fig. 83) has published a photomicrograph of the fore-brain of a 16 mm. 

 human embryo Se, in which the two halves of the brain were not sectioned symmetrically, 

 so that different levels appear on the two sides of the median line. Fortunately, on the 

 left side the cavum laterale corporis striati occurred in the plane of section. It is roughly 

 piriform, the pointed extremity being directed toward the cerebral ventricle, while the blunt 

 end approaches the surface of the striate body. This illustrationof the lateral cavity is very 

 similar in its position and size to those illustrated in figure 7, which is photographed from 

 embryo 409, a specimen of exactly the same length as Se. The lateral cavity usually develops 

 before the medial, so that it is safe to predict that the His embryo would show another 

 cavity more deeply placed in the striate body if the plane of section had not been so oblique. 



The accompanying list of embryological material from the Carnegie Institution of 

 Washington includes all the specimens from 15 mm. to 23 mm. (crown-rump length) which 

 permit of histological study. With but one exception, evidences of one or both sets of 

 cavities have been found in the corpus striatum. 



The cavities in the corpus striatum fall into two groups — one appearing very near the 

 lateral surface of the brain, the other occupying a medial position within its substance. 

 Generally each is but a single cavity, and all of the smaller diverticula communicate with 

 the main cavity. Either, however, may be represented by multiple cavities wholly uncon- 

 nected with one another, yet so close as to be separated only by a thin partition of nervous 

 tissue. As it lies deep in the striate body, the medial cavity tends to be more smooth-walled 

 than the lateral. The latter is frequently traversed by numerous blood-vessels having a 

 thin layer of neuroblasts adhering to their walls; small strands of nerve-cells stretch like 

 spider-webs from one wall to another. In addition to the cavum mediale and cavum 

 laterale an intermediate group is present in one specimen, situated midway between the 

 two. In all of the specimens studied the medial group appears in younger embryos than 

 does the lateral, and disappears first in some of them. There are embryos of 24 mm. in 

 which both cavities are still well developed. 



No direct communication between these cavities and the vascular system could be 

 made out. In none of the four injected embryos included in this study (No. 390, 15.5 mm. ; 

 No. 424, 17.2 mm.; No. 460, 21 mm.; No. 382, 23 mm.) was there any tendency for the 

 injected mass to flow out into these spaces, although vessels containing granules of injection 

 coursed directly through the cavity. In one instance (embryo 460) a small amount of 

 India ink backed into the cavum laterale from an extensive subpial extravasation. When 

 erythrocytes have been found in these spaces the cavity has shared in a generalized extrava- 

 sation of formed elements throughout the entire head. 



