184 EDWARD L. RICE 
minates with a curved margin, which forms the anterior limit of 
the enormous fenestra olfactoria (fen.ol.). The lateral boun- 
daries of this fenestra are formed by the sphenethmoid cartilages 
(c.sph-e.), converging backward from the lateral margins of the 
nasal roof to unite with the narrow anterior end of the solum 
supraseptale of the orbital region. Extending through the 
middle of the fenestra olfactoria is the free dorsal margin of the 
septum, in the region of transition from interorbital to nasal, 
dividing the fenestra into symmetrical right and left halves, and 
in each of these halves is the vertical wall which forms the true 
. posterior limit of the nasal region—the planum antorbitale 
(pl.ant.). Septum and sphenethmoid cartilages form the sole 
connection of the ethmoid region with the posterior regions of 
the skull. 
It is convenient to divide the ethmoid region transversely into 
three parts of approximately equal length. This threefold divi- 
sion is an essentially morphological one and corresponds with 
that employed by Gaupp for Lacerta and the Amphibia. The 
posterior third, determined by the extraconchal recesses, is much 
the broadest of the three. Its real division from the middle 
third is marked by the depth of the conchal infolding, into which 
the aditus conchae leads, although laterally the extraconchal 
portion extends considerably further forward, overlapping with 
the middle third of the ethmoid region. The anterior third is 
related to the external nostrils, and is the narrowest of the three 
regions. It is divided from the middle third by a rather con- 
spicuous lateral notch, just behind the superior alar process 
(fig. 3, pr.al.s.). Between this notch and the conchal infolding 
the middle third expands to a width intermediate between that 
of the anterior and that of the posterior third. This region is 
the zona annularis of Gaupp. The enormous fenestrae supe- 
riores nasi (fig. 1, fen.s.na.) lie mainly in this division, but extend 
slightly into the anterior third. 
