298 
poral bone” reduced, in human anatomy, mainly to the support of the tympanic mem- 
brane. The feebly marked groove and ridge on the hind concavity of the tympanic 
intimates the degree in which the function in relation to the organ of hearing is 
exercised in the ornithic modification of the air-breathing vertebrate tympanic bone. 
The vertical length of the present tympanic is 1 inch 25 lines; the long diameter of the 
distal articular surface is 1 inch; it is slightly convex, but by a downward production of 
the middle of the outer border is there made concave transversely at the outer half. 
The mandible of Aptornis presents in profile (Pl. LXXXIIL. fig. 1, 29-82) a series of 
graceful curves. By the downward production of the angle (30) and the elevation of the 
articular surface (29), it is curved for a short way with the concavity below, then becomes 
concave above for a longer extent, and finally is again bent with the concavity downward, 
The extent of the symphysis (Pl, LX XX TY, figs. 6, 7, 32) is 2 inches, following the curye, 
rather more than one-fourth the length of the mandible; its upper surface (ib, fig. 6, 32) 
is longitudinally convex, transversely concave, deepening, as it widens, backward, ‘The 
hinder half of this concavity is smooth; the fore half shows two parallel longitudinal 
neryo-vascular tracts, with canals leading forward and opening upon the outside of the 
symphysis near the end; this has a horizontal, subtrenchant, slightly convex border. 
The dentary margins are rather sharp as they extend backward for an inch and a half, 
then begin to thicken into a convex border, 14 line across, which border again contracts 
before it is lost in the thick hinder half of the ramus. ‘he outside of the trenchant 
margin of the symphysis is indented by a delicate line. An oblique groove, beginning 
about the middle of the outside of the ramus, indicates the junction of the dentary 
(Pl. LXXXIII, fig, 1, 32*) with the angular element (30), which is further denoted by a 
ridge continued backward from the groove. <A fissure on the upper border of the ramus, 
half an inch in front of the articular surface (Pl. LX XXIV. fig. 6), sinks into the sub- 
stance of the bone as it advances, and opens by a shorter fissure upon the inner surface 
of the ramus nearly two inches from the angle. ‘The tract between the two fissures pro- 
bably included the hind end of the splenial. Save at these indications all the elements 
of the mandible are fused into one bone of a strong, compact osseous tissue, as in a few 
other strong-billed birds. The articular surface is single (Pl. LK XXIV. fig. 6, 29) with 
the moderate convexities and concavity of its undulated surface answering to those on the 
tympanic. ‘The fore-and-aft diameter of this surface of the mandible is 7 lines, the trans- 
verse diameter is TZ lines. I never saw a mandibular condyle of an oviparous Vertebrate 
in which so large a proportion was convex. Behind the articular surface there is a very 
small and not deep fossa; internal thereto the bone extends obliquely upward and inward 
into an irregular conical process, attached by ligament to the posterior non-articular part 
of the mandibular end of the tympanic. The outside of the ramus, below the articular 
surface, is strengthened by a tuberous ridge, between which and the angle is a broad 
oblique channel. There is no “coronoid” elevation; the ramus rather loses than gaius 
} e . . 
Ramphastos, Buceros, Psittactd, Baleniceps. 
