1888.] 



the Skeleton of the Apteryx. 



393 



can be drawn between ali-ethmoidal, ali-septal, and ali-nasal, any more 

 than between mesethmoid, septum nasi, and pre-nasal. The dorsal 

 border of the mesethmoid, from anterior end of crista galli to within 

 about 2 cm. of end of beak, sends off horizontal plates on each side, 

 which pass at first outwards, then downwards, and finally, in part of 

 their extent, inwards, thus forming roof, outer wall, and in part floor 

 of the nasal chambers. 



The precise relation of these lateral ethmoidal plates varies in 

 different regions, and it is convenient to consider them as consisting 

 of five portions. 



In the first or posterior portion, besides passing outwards and down- 

 wards, they take a sweep backwards, and then inwards, thus forming 

 an almost complete somewhat shell-like covering for the principal or 

 inter-orbital portion of the olfactory capsules. To this portion the name 

 ali-ethmoicl may he applied. Each ali-ethmoid is a thin plate of carti- 

 lage, convex externally, forming the outer border of the cribriform space 

 (olfactory foramen) by its dorsal free edge, and closely applied below 

 by its ventral edge to the mesethmoid, immediately dorsad of the 

 rostrum ; in front it is continuous laterally and dorsally with the 

 second portion, and ventrally ends irregularly, presenting a deep ante- 

 rior emargination, which separates a slender, forwardly directed 

 process (c) from the main ali-ethmoidal cartilage. 



In its second portion the lateral ethmoidal cartilage furnishes only 

 roof and sides to the nasal chamber, the floor being absent, and thus 

 the turbinals are visible from below. 



In its third portion it again turns inwards so as to furnish a floor 

 to the nasal cavity, in the form of a plate with a straight lower 

 border abutting against the mesethmoid, and with oblique anterior 

 and posterior edges. 



In their fourth portion the lateral ethmoids again furnish only roof 

 and outer walls to the off- chamber, and in their fifth or anterior 

 portion, they are entirely unconnected with the mesethmoid (pre- 

 nasal), and form two slightly divergent obliquely placed plates of 

 cartilage which are continued to the end of the beak, passing dorsad 

 of the nostrils. To these the name ali-nasals might be applied, but 

 owing to the unique position of the anterior nares, the relations of 

 these and other parts of the ethmoidal region is strikingly different 

 from what we are familiar with in other birds. 



There is a single ethmoidal ossification, mesethmoid, in the form of 

 a bone composed of horizontal and vertical portions and T-shaped in 

 transverse section. The horizontal portion is shield-shaped, and 

 appears on the surface of the skull between the posterior ends of the 

 nasals : the vertical portion ossifies the whole postero-dorsal region of 

 the mesethmoid : the bone in question is therefore partly mes- and 

 partly ecto-ethmoidal. 



