240 D. DAVIDSON BLACK 



He does not describe any connection between the remains of 

 the third ventricle and the cavity of the cerebral vesicle. From 

 his figures I am led to believe that this connection was inter- 

 rupted. The attachment of the thalamus to the cerebrum was 

 very slight and wholly basal. Into this region, projection fibers 

 converge from the lateral nuclei of the thalamus, constituting an 

 atypical thalamic radiation. Ventrally the fibers of the two 

 sides decussate and end blindly in the basal region of the cere- 

 brum, which before has been alluded to as the probable repre- 

 sentative of the corpus striatum. 



It is thus seen that, as in the present case, the third ventricle 

 has been considerably reduced in volume and its connection with 

 the cavity of the cerebral vesicle has also apparently been entirely 

 interrupted. 



A single median optic nerve was present which divided pos- 

 teriorly at a partial decussation into paired optic tracts. In- 

 fundibulum, corpora mammillaria and lateral geniculate bodies 

 could be distinguished and a commissure of Meynert is described 

 crossing in the tuber cinereum. Dorsally the habenular bodies 

 were prominent, together with the posterior commissure and fas- 

 ciculus retroflexus of Meynert. Medullated fibers were found in 

 the taenia thalami (stria medullaris thalami). 



The thalamic nuclei were not definitely marked out, but the 

 whole thalamic mass was relatively rich in well formed ganglion 

 cells together with more numerous embryonic elements and neuro- 

 blasts, being thus similar in these lespects to the present case. 



From the region of the interpeduncular ganglion caudad, the 

 brain stem was much distorted by a malformation quite inde- 

 pendent of the cyclopian condition. A split had occurred in 

 the mid-line, resulting in a more or less complete separation of 

 the brain stem and cerebellum into right and left halves. Rela- 

 tions were further complicated by the presence of an additional 

 flexure in the brain stem and by the bending dorsally of a con- 

 siderable portion of the split cord so that it came to lie upon the 

 malformed brain stem halves within the skull cavity. A con- 

 siderable amount of fusion between the cord and underlying 

 brain stem halves was also present. 



