632 GEOLOGICAL SURVEY OF THE TERRITORIES. 
form a portion of the flcor of the orbit on either side. The union 
among the basi-presphenoidal process 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 maxilliary articulation 
to the tympanic, about 4 millimetres, the skull being horizontal. 
The coalescence among its three original elements is unusually per- 
fect. The 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-pala- 
tine with the rostrum of the basi-sphenoid. In our present subject, 
as in Pica and Corvus 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 ros- 
trum, the two bones not usually coming in contact. The shaft of 
the pterygoid also slightly expands horizontally just before this artic- 
ular 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 bone 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 ptyergoidal 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 development of pterapophysial processes is to be observed. Asis 
generally, though by no means universally, the case among birds, the 
mastoid process of the tympanic 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 surfaces, the outer and at 
the same time the anterior looks outwards, forwards, and upwards, while 
the inner and posterior one, snrmounting the shorter limb or bifurcation, 
looks backwards and upwards. These two projections of the mastoid 
process are further separated posteriorly by a deep non-articular de- 
pression. The orbital process is well developed, long and slender, ter- 
minating in a knobbed extremity, the whole extending well within the 
orbital space. It has at its base, internally, the facette for the ptery- 
goid already alluded to. This process is subcompressed from before 
backwards, and has throughout a gentle curvature upwards, having 
much the form of the thorn of the common rose, without its sharp point. 
There are two articular facettes on the inferior side of the mandibular 
end, divided by rather a deep depression. Of the two, the inner is the 
larger and more symmetrical in form, being transversely elliptical. The 
outer one seems to be borne on rather a constricted neck, having on its 
outer aspect the acetabulum for the hemispheroidal facette on the squa- 
mosal. The anterior surface of the body is smooth and triangular in 
outline; the opposite and inner surface, somewhat similar in appearance, 
ee 
