31 
toral” ridge (PI. VI. fig. 1, kf is feebly indicated, extending from the onter end of the 
coracoid groove backward and inward to near the posterior third of the keel. The con- 
cave surface of the sternum (ib. fig. 2) shows a number of small pneumatic foramina, 
chiefiy along the middle line to near the posterior third. Behind the costal border the 
substance of the sternum gradually increases in thickness from the sharp lateral margins 
to the middle, above the base of the keel, and shows there a fine pneumocancellous 
texture (PI. XI, fig. 4). 
Scapular Arch. (Plates III. & VIII.) 
This consists of the scapula (PI. VIII. figs. 6 , 7, 8 & 9, 51 ), coracoid (ib. figs. 4 & 5, 5 .), and 
clavicle (ib. 5 s), the latter ending in a point and here tied by ligament to its fellow, to form 
a furculum. I have received the elements of this arch in three conditions : — one in which 
the bones, though of full size, are separate ; a second, in which the scapula and coracoid 
are confiuent, but the clavicle distinct ; a third, in which the three bones are confiuent 
at the ends converging to the humeral articulation. The scapula (ib. figs. 6, 7, 8 & 9, 
51 ), 3 inches 7 or 8 lines in length, has the usual sabre-shaped body, slightly expanding 
and decurved at its free extremity, the breadth of which is 7 lines : it terminates ob- 
tusely : varieties of shape are shown in figures 6 & 8. The outer surface of the bone, 
at the two posterior thirds of its extent, is slightly concave and marked by muscular 
attachments ; the inner surface of that part is smooth and slightly convex : the bone 
increases in breadth, with some diminution of thickness, towards the articular end, and 
is remarkable for sending off from the lower border, at 7 or 8 lines from that end, 
a short process (ib. 5i) ; between this process and the articulation the breadth of the 
bone is little more than 3 lines ; the breadth of the articular end is 9 lines. Nearly 
one-half of it is occupied by the almost fiat, subcircular humeral surface (fig. 8, a), with 
a diameter of 4^ lines, and directed upward, outward, and a little forward. From this is 
continued an oblong, much narrower coracoidal surface, beyond which the acromial pro- 
cess (fig. 6, c) extends forward, curving toward the coracoid, and terminating obtusely. 
The coracoid (ib. figs. 4, 5, 8 & 9, 52 ), averaging a length of 3 inches 7 lines, expands 
to a breadth of I inch 3 lines at its sternal end ( 52 ), of which the articular surface [e) 
occupies an inch ; the non-articular part forms the outer angle (m), and extends in advance 
of the pneumatic foramen (PI. IV. fig. 4, p) at that part of the breast-bone : the outer 
border which extends from this free angle to the body of the bone, into which it subsides, 
at one-third of the extent of the bone, is sharp ; the inner border is obtuse to near the 
inner angle (PI. VIII. figs. 4 & 5, n). The outer surface of the expanded sternal end 
is smooth and convex; the inner surface is flatter and more irregular, perforated by 
pneumatic foramina ; the diameter of the subcylindrical part of the shaft is 4 lines : the 
extremes of ditference in the distal expansion of the coracoid are shown in figs. 4 & 8, 52, 
' The intermuscular ridges (‘ pectoral,’ ‘ subcostal,’ ‘ oarinal ’) are, with other parts of the bird’s sternum, 
here named as defined in my ‘Anatomy of Vertebrates,’ vol. ii. pp. 16-23. 
