Coe and Kunkel— California Limbless Lizard. 389 
of these lie in the middle line, the post velar arch immediately 
behind the paraphysis, and separated from the latter by only the 
velum transversum (v.t). These evaginations are somewhat con- 
stricted at their bases but become slightly wider distally, forming 
long tubular sacs. The velum hangs down from the dorsal wall of 
the ventricle in a transverse position and bears a commissure (¢.@) 
at its free distal end. 
The exact significance of this commissure has not yet been deter- 
mined. There can be but little doubt that what has here been 
termed the velum transversum is actually that structure. The velum 
has a position immediately posterior to the paraphysis and anterior 
to the post velar arch throughout the Vertebrate series. v. Kupffer 
(793) figures a sagittal section of the brain of a four weeks embryo 
of Acipenser which shows this relation. De Graaf (’86a) does the 
same for Triton. In the lizards this structure is also described by 
Burckhardt (94) in an embryo Zacerta. <A similar structure is 
shown but not named in a number of Baldwin Spencer’s drawings 
of the epiphysis of adult lizards. Francotte (’88) gives photo- 
micrographs of sagittal sections of the brain of Anguis which show 
the velum and the structure running along its distal margin very 
much as in Anniella, but he does not mention the commissure in his 
description. The only reference we have seen to a commissure in 
this situation is by Rabl-Riickhard (’81), who finds in the brain of 
Psammosaurus terrestris such a structure lying immediately behind 
the connection between the third and the lateral ventricles, the fora- 
men of Monro, and having the form of a small bundle of fibers 
stretching across the narrow cavity of the third ventricle and lying 
upon the dorsal surface of the optic thalami. Rabl-Riickhard con- 
siders it to be a rudiment of the posterior portion of the fornix and 
homologous with the transverse tract of fibers of the same. As 
Rabl-Riickhard has no figure of the structure in question, it is impos- 
sible to be certain about the homology, but from his rather brief 
description this commissure corresponds closely with the rudiment of 
the fornix and will be so designated for the present. 
The post velar arch is a simple unbranched tubular sac which 
extends slightly posteriorly and dorsally and lies immediately in 
front of and in partial contact with the epiphysis. The cells (pl. xtv1, 
fig. 44, e’) forming this sac are slightly differentiated from the epen- 
dyma cells (fig. 45, e) in shape and staining qualities, being more 
nearly cubical and exhibiting nuclei which do not stand out as sharply 
from the cytoplasm as in the ependyma proper. The cytoplasm is 
rather denser and the nuclei do not take the nuclear stains so readily. 
