A CASE OF CYCLOPIA 221 



In the anterior portion, the dorsal area is divided into two large 

 irregular lateral nuclei {Nu.lat.Th., figs. 41 to 46) and a smaller 

 mesial nucleus {Nu.med.Th.). 



Caudally the lateral nuclei are further subdivided so that it 

 is possible to distinguish three nuclei in this region. These may 

 be termed for descriptive purposes, dorsal (Nu.lat.l), lateral 

 {Nu.lat.2), and central {Nu.lat.3) nuclei of the lateral mass. The 

 mesial nucleus (Nu.Med.Th.) is present in the caudal portion in 

 essentially similar relations. 



It is to be noted that these thalamic nuclei do not come into 

 relation with the cortex cerebri at the junction of the thalamic 

 mass and the cerebral vesicle, but are separated from it by the 

 ventral thalamic radiation. 



The ventral fibrillar area. This area occupies but a small 

 space in sections through the more caudal part of this region, 

 but increases in size as one passes forward by the addition of 

 fibers arising in the dorsally placed nuclei. It is made up of a 

 complex of both medullated and nonmedullated nerve fibers, 

 which, in the caudal portion, are twisted into irregular whorls 

 and tangles. It is remarkable that, in this region, irregular 

 strands of poorly medullated fibers may be seen in numerous 

 places piercing the outer limiting layer of neuroglia in*the ven- 

 tral region and ramifying within the thickened pia (/3, figs. 42 

 to 44). 



Passing forward, the thalamic mass becomes united to the 

 cerebral vesicle by a narrow peduncle. This peduncle is seen 

 to be made up almost entirely of ventrally coursing fibers con- 

 tinuous posteriorly with those of the ventral area of the thalamic 

 mass. These fibers must be taken to represent an atypically 

 developed thalamic radiation (Rad.Th., figs. 41 to 47). 



The major portion of the fibers of the thalamic radiation are 

 applied to the ventral surface of the cerebral vesicle on which 

 they rapidly spread out and come to an end. The ventral sur- 

 face of the cerebral vesicle represents the free surface of the cor- 

 tex. Thus most of the fibers arising in the thalamic mass {Rad. 

 Th.) pass directly into the zonal or plexiform layer of the cere- 

 bral cortex (/Si.s.j'figs. 46 to 47). 



