SKELETON OF PHOROEHACOS INFLATTTS. 



67 



The dimensions of the mandible are : — 



cm. 



Total length 30-2 



Length of symphysis 9*0 



Depth of ramus at coracoid process 4'9 



Width of articular end . 5 - 5 



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. 



Z. 



ENT.GL. ^___^_^=, B.HY. 



A. 



3. 

 Hyoid of Phororhacos inflatus Ameghino, slightly reduced. 



1. From below. 



2. Basihyal from side. 



.?. Section of entoglossal at point A. 



ent.gl., entoglossal ; b.ht., basihyal (first basibranchial) ; c.br., cerate-branchial. 



articulation for the basihyal (basibranchial 1) (b.ht.), 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 



