CHONDROCRANIUM OF EUMECES iréal 
small remnant of the septum, the cartilago hypochiasmatica 
(fig. 3, c.hyp.), over which the optic nerves cross in passing to 
the orbits (fig. 28, n.JI.ch. and c.hyp.). In Dermochelys Nick 
describes a closed fenestra in place of the more characteristic 
notch between the cartilago hypochiasmatica and the fused 
trabeculae; a similar condition is noted by Kunkel (712 b) as a 
temporary stage in the formation of the notch in Emys. The 
cartilago hypochiasmatica is described by Gaupp as cylindrical 
(‘drehrund’) in Lacerta; in Eumeces it is a flattened vertical 
plate. A minute transverse perforation appears to have no 
special significance. The connection of the cartilago hypo- 
chiasmatica with the subiculum infundibuli and the lateral wall 
of the temporal subregion is discussed later (p. 176). 
In stage 5 of Eumeces, as in Lacerta, the septum interorbitale 
is not a continuous structure, but is interrupted by an enormous 
fenestra (figs. 3 and 24, fen.sep.) in its upper portion just below 
the union with the solum supraseptale. In fact, so far as the 
septum itself is concerned, this is a deep dorsal notch rather 
than a true fenestra, for its upper boundary, in the posterior 
part, is formed not by the septum, but by the solum supra- 
septale (fig. 24). In Lacerta Gaupp figures another fenestra a 
little further forward, just at the transition from septum inter- 
orbitale into septum nasale. If there be such a second fenestra 
septi in stage 5 of Eumeces, it is very minute and limited to one 
or two sections; at best, its presence is questionable. On the 
other hand, there is unquestionably an area in which the cartilage 
of the septum is conspicuously thinned; in a later embryo, 
stage 6, this thinner area is replaced by a fenestra of considerable 
size. The position of this thin area or fenestra is rather more 
anterior in Eumeces than in Lacerta, falling in the ethmoid 
rather than the orbital region. It is improbable that these 
fenestrae have any essential morphological significance, but as 
the external signs of the forces influencing the development of 
the skull they may be of considerable import. In this connec- 
tion further comparison of different developmental stages proves 
interesting. In stage 5 a second thin spot is noted in the septum, 
immediately below the principal fenestra septi (fig. 24), and in 
