ce) Osteology of Circus hudsontus. 
The mandible may be said to partake of the V-shaped variety, 
although its inner outline borders closely on the U (Figs. 1 and 6). 
The symphysis is gently curved down anteriorly so as to look 
upwards and forwards. Each ramus has rounded superior and 
inferior borders, and their width is quite uniform from the cor- 
onoid process to symphysis on either side (Fig. 1). 
Upon this aspect, too, we observe that the ramal vacuity, seen 
in so many birds, indeed in other Hawks (falco), has here been 
entirely absorbed. Every evidence of original sutural landmarks 
has been obliterated, and the mandible of this Hawk is as good 
an example as we will find anywhere among the class of a ‘‘ single 
bone.’’ One not acquainted with its com- 
position in the nestling would never sus- 
pect anything else after a careful examina- 
tion. ‘The in-turned tips of either articular 
end is at right angles to the median plane. 
Each presents an elliptical pneumatic fora- 
men just within the tip. Concave articular 
facets are seen, which correspond to the 
convex surfaces, as described on the foot 
of each quadrate. There is a rudimentary 
‘‘ posterior articular process ’’ present. The 
Bos thsi oe coronoid process, on either ramus, is but 
seen ot aetye, 7 ite feebly developed and only slightly elevated 
above the general line (Fig. 1). When 
articulated with the skull the superior line of the ramus ceases to 
be approximated to the osseous superior mandible at a point on 
the middle of the dentary process of that bone. From this point 
it curves gently downwards until at the tips of each mandible 
they are four millimetres apart. This condition is seen in the 
Cathartide also. (See author’s ‘‘ Osteology of the Cathartide,”’ 
ies. TO5; 100, 1hs and. nnG,) 
On the hyoid arches we find that the glosso-hyal remains in 
cartilage throughout life (Fig. 4). The cerato-hyals or ‘lesser 
cornua’’ are quite individualized, being simply connected by a 
transverse bar at their middles, affording the articular facet for the 
basi-hyal. ‘This letter element is co-ossified with the basi-branchial 
or uro-hyal, the two bones forming one piece in the adult Hawk. 
The cerato and epibranchial elements are up-curved, slender, cylin- 
drical rods of bone, the latter being slightly tipped on their poste- 
