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bearino; 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 {M.E., M.E.^, figs. 1, 3).— Presumably 

 an ossification of the ethmoid cartilage. In front it bears 

 a prominent beak {M.E.^), 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 diverting 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 [Eth., figs. 1, 2, 3). — 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 



