4 Osteology of Circus hudsontus. 
always to be found a free ‘‘ accessory piece’’ consisting of asmall 
osseous scale, horizontally attached to the bone by a semiliga- 
mentous tissue. 
The lacrymal of C7vcus is a thoroughly pneumatic bone, and 
presents for examination several confluent foramina, which open 
on its inner aspect at the junction of the supercillary and desend- 
ing processes. 
The anterior border of the superior half of the e¢imozd is broad, — 
flat, and somewhat thickened ; and this part of the bone reaches 
forward beyond the aliethmoid plates, to form a substantial base 
upon which the frontals and premaxillary rest. Anteriorly, the 
lower margin of the ethmoid is sharp where it joins with the 
rostrum. 
The aliethmoid plate is conspicuous on lateral aspect of the 
skull. Its posterior surface looks upwards, backwards and out- 
wards, the plane being reversed for the anterior surface. In outline 
it is an oblong plate, which is quite true for its lower and free end, 
while the opposite end is broader and merges with the mesethmoid. 
At its superior and inner angle, just beneath the frontal, it is 
pierced by an elliptical foramen for the passage of the olfactory 
nerve. Beyond, it develops a small bony canal for the further pro- 
tection of this branch. The interorbital septum presents near its 
middle one large, elliptical vacuity, with the major axis of the 
ellipse about parallel with the zygomatic bar. 
In the recess of the angle between this septum and the frontal 
bone, we find the double groove for the lodgment of the olfactory 
nerve, the grooves commencing directly in front of the olfactory 
foramen, running parallel with each other quite up to the opening 
for their passage through the aliethmoidal plate. The zygomatic 
or jugal bar is very slender in C?7czs, and the sutures of its original 
elements are quite obliterated. Its quadrate end develops at right 
angles a peg-like process, to articulate in a corresponding pitlet in 
that bone. The maxillary or anterior extremity has already been 
sufficiently described. Its relations with the palatines and max- 
illo-palatines are well shown in Fig. 3. 
The superior margin of the orbit is rounded, but as this pro- 
ceeds backwards it soon becomes sharp, a condition it retains to 
the very tip of the sphenotic process. 
At the back of the orbit the wall is broad and gently concave 
throughout ; it being pierced at its lower and inner angle by a 
