SKELETON OF PHORORHACOS INFLATUS., 67 
The dimensions of the mandible are :-— 
cm. 
Totalllenstheeiun! acme niles! +) Coats ati thee edn ene MOOs2 
ITEANORe AMIS 5 5 o a of 6 p oo 6 oho G 5 a, /GHo 
Depth of ramus at coracoid process. . .... 2.2... «49 
WGho@rennenbe Gicl G 5559 6 6 6 6 a oo 6 68 5 6 Ate 
The hyoid (text-figure, below) is very well preserved, a most exceptional, if not 
unique, circumstance in a fossil bird. The anterior element, the entoglossal 
(ENT.GL.), is very large and clearly has originated from the union of two rod-like 
elements, the ceratohyals, which are united by a thin plate of bone. On the ventral 
surface the division between the rods is marked by a deep furrow, deepening posteriorly, 
but the dorsal surface seems to have been regularly convex from side to side. ‘The 
anterior end is somewhat broken; the posterior is deeply divided by a double 
Fig. 4, 
Hyoid of Phororhacos inflatus Ameghino, slightly reduced. 
1, From below. 
2. Basihyal from side. 
2. Section of entoglossal at point A. 
ENT.GL., entoglossal ; B.Hy., basihyal (first basibranchial) ; c.pr., ceratobranchial. 
articulation for the basihyal (basibranchial 1) (B.uy.), and laterad to this the outer 
angles are produced into short backwardly-directed processes. 
The first basibranchial (B.Hy.) (basihyal) is a short bar of bone, the thinner lateral 
borders of which seem to have been broken away. Its dorsal surface is concave from 
before backward, and on its anterior half from side to side also; ventrally it is convex 
from before backward. ‘The anterior end bears a double surface for articulation with 
the entoglossal, separated by a slight ridge, which at its ventral extremity is produced 
into an anteriorly-projecting prominence. Posteriorly there are two irregular surfaces 
for the ceratobranchials, meeting at an angle of about 120°. The first basibranchial is 
not prolonged backward into a urohyal, nor does it, as far as can be seen, bear any 
surface for the articulation of a distinct median element: if such were present it must 
