498 DR. R. O. CUNNINGHAM ON THE ANATOMY 
Ducks, e.g. the Mallard. The nasal processes of the intermaxillary are only very 
slightly anchylosed to one another and to the nasal, even in the oldest specimens. 
All the elements of the lower jaw, i.e. articular, angular, coronoid, opercular, 
splenial, and dentary, are readily separable in the unfledged birds. In the adolescent 
specimens the articular, opercular, angular, and coronoid have coalesced to form one 
piece, while the splenials and dentary are still distinct. In adult birds sutures still 
persist between the first three elements and the posterior portion of the splenial, and 
between them and the posterior portion of the dentary. The extreme length of the 
mandible in the largest adult specimen examined is five inches and a tenth. 
The hyotd is of the usual form which obtains in the Anatidee. The glosso-hyal bone 
in an adult specimen measures rather more than an inch and a tenth, in length. Its 
upper surface is concave antero-posteriorly, but convex from side to side. The carti- 
lage borne at its tip is cylindrical, and nearly an inch in length when recently freed 
from the surrounding soft parts. The basihyal and cartilaginous uro-hyal measure 
respectively one inch, and half an inch, in length. The rami of the hyoid are three 
inches and a half in length, measured along the curve, the hypobranchial bones fur- 
nishing the greater part of the extent. 
Vertebre. There are twenty-one free vertebre between the cranium and pelvis, and 
of these the last six are rib-bearing. The seventeenth, eighteenth, nineteenth, and 
twentieth have elongated hypapophyses. Owing to the anchylosis of the pelvic ver- 
tebre it is not easy to form a perfectly accurate estimate of their number, which is 
probably seventeen. ‘The combined mass is only united synchondrosially to the iliac 
bone of either side even in flying birds, and is consequently easily separated from them 
(see fig. 59). The first three vertebre are rib-bearing. The caudal vertebre are nine 
in number; but the eighth and ninth become anchylosed in adult birds. 
ibs. There are nine pairs of vertebral ribs, of which the last eight articulate with 
the corresponding sternal ribs. 
Sternum and shoulder-girdle. The sternum is of large size, measuring fully five inches 
and a half in extreme length in adult specimens. It is thus nearly equal in length 
to that of the Muscovy; but it is much broader, the distance between the tips of the 
anterior costal processes being three inches and three-tenths, and a little over two inches 
and a half between the posterior costal processes. In general form and shallowness of 
keel it approximates more closely to the sterna of Oidemia nigra and Biziura lobata 
than to those of the other Anatide examined by me. In adult species the posterior 
border is more deeply excavated than in adolescent (flying) birds. On removing the 
pectoral muscles from the sterna of the flying birds I found on all occasions a layer of 
perichondrium of greater or less thickness covering the subjacent bone, which was 
much thinner, rougher, and more vascular than in adult birds. In one specimen of a 
full-grown bird in the Museum of the Royal College of Surgeons, there is present on 
either side of the keel, at a distance of about an inch and a third from the sterno- 
