19 
bearing it is also the smaller of the two (cp. fig. 1). Above 
the olfactory foramen the left prefrontal is prolonged 
upwards and backwards to assist the median ethmoid in 
forming the anterior boundary of the left orbit. This 
process is practically absent on the right side. The pre- 
frontal, which is called by other authors ectethmoid, 
lateral ethmoid, parethmoid, or paired ethmoid, is bounded 
by the lachrymal, vomer, mesethmoid, ethmoid cartilage, 
and frontal, the left one further by the parasphenoid. 
Mesethmoid (J/./., M.E.}, figs. 1, 5)—Presumably 
an ossification of the ethmoid cartilage. In front it bears 
a prominent beak (4/./.!), and above this is a depression, 
both of which are connected with the motion of the inter- 
maxillary cartilage. The marked inclination of the 
former to the eyeless side will be noted, thus civerting the 
motion of the jaws to that side. Behind, the mesethmoid 
is laminate, and takes a sharp turn upwards, forming by 
a graceful curve the anterior wall of the left orbit, the 
remainder of which is contributed by the left prefrontal. 
In front and on each side of the mesethmoid the ethmoid 
cartilage appears on the surface of the cranium, whilst 
behind and above on the right is an attachment for the 
right nasal. The mesethmoid is bounded by the vomer, 
ethmoid cartilage, prefrontals, right nasal and right 
frontal. 
Ethmoid Cartilage (Wth., figs. 1, 2, 5)—An asym- 
metrical unpaired cartilage quite separable in the 
macerated skull except for those portions embedded in the 
prefrontals. It consists of two parts, one a long basal 
horizontal rod tapering to a point behind and fitting into 
a deep groove on the upper surface of the parasphenoid 
alongside the caudal process of the left prefrontal, the 
other a vertical plate with a marked deflection to the 
ocular side and perforated by a large fenestra. The latter 
