No.5.\ SHUFELDT ON THE OSTEOLOGY OF EREMOPIIILA. 125 



velop two other slender horizontal x>lates, the superior one being pro- 

 longed forward as a fine spicula of bone to meet the ethmo-turbinal mass, 

 as above described. 



They lightly touch the rostrum of the sphenoid, in comi)any with the 

 pterygoids, forming the usual arthrodial joint at thifi point in avian 

 structure. Above they are smooth, look upwards and outwards, and 

 form a portion of the floor of the orbit on either side. The union among 

 the basi-presphenoidal process, vomerine, and prefrontal plates is com- 

 plete, all sutural traces having disappeared, and the included bones form 

 the interorbital septum as already described. The zygomatic style? 

 very slender, straight, and throughout its continuity nearly of uniform 

 calibre, descends from before backwards from its maxillary articulation 

 to the tympanic, about 4 millimetres, the skull being horizontal. 



The coalescence among its three original elements is unusually per- 

 fect. Its anterior horizontal expansion is very slight, being crowded 

 towards the intermaxillary osseous tomium on either side by the widely 

 separated palatines. 



Its posterior extremity is club-shaped and turned upwards, bearing 

 on its inner aspect a hemispheroidal articular facette for the cotyloid 

 cavity of the tympanic. In no single articulation found in the skeleton 

 throughout the class does there seem to be more variation in plan, to 

 meet the same end and carry out the same function, than we find in the 

 pterygo-palatine with the rostrum of the basi-sphenoid. 



In our present subject, as in Pica and Gorvus and many others, this 

 extremity bears a thin expansion that articulates by its anterior edge 

 with the palatine plate and neatly grasps the rounded and inferior side 

 of the rostrum, the two bones not usually coming in contact. The 

 shaft of the pterygoid also slightly expands horizontally just before this 

 articular surface is developed, more particularly in the angle between 

 the two, adding greatly to the strength of the bone, and somewhat to 

 the floor of the cavity of the orbit. The angle of divergence of the 

 pterygoids in the present instance is exactly 45° ; the intertympanic 

 chord, 7 millimetres. The shaft of this bono is comparatively slender, 

 prismoidal in form, somewhat twisted, and develops among the older 

 birds sharp projecting edges. The enlarged tympanic extremity bears 

 a subelliptical articulating facette, that glides upon a similarly formed 

 surface surmounting the pterygoidal process at the base of the orbital 

 process of the corresponding tympanic element. These two little bones 

 are well separated from the basi-sphenoid, and never any evidence of 

 the develoi)ment of pterapophysial processes is to be observed. As is 

 generally, though by no means universally, the case among birds, the 

 mastoid process of the tymjmnic in this Lark is distinctly bifid, each 

 limb presenting for examination at its extremity an elliptical convex 

 facette for articulation in a cup-shaped cavity intended for its reception 

 in the roof of the aural vacuity. Of the two surfiice?, tlie outer and at 

 the same time the anterior looks outwards, forwards, and upwards, while 



