different. The last few tracheal rings are incomplete posteriorly; the space left between them is continuous with a membrana tympaniformis. There is no pessulus or intrinsic musculature; in the division of the last tracheal rings there is a suggestion, faint perhaps, of the tracheal syrinx. Dromæus, as might be imagined, closely resembles Casuarius. It has, however, a peculiarity which has been fully gone into by MURIE,' who quotes the pre-existing literature upon the matter. In front of the trachea some way down the neck a certain number of the tracheal rings are deficient in front; and the lining membrane of the tube here projects as a sac, which can be inflated, and has, no doubt, something to do with the drumming voice of the bird. The accompanying illustration shows this peculiarity, which is not met with in the cassowary.2

As to osteology,3 in Rhea (fig. 77, p. 140) the vomer tends to be bifurcate posteriorly where it is much widened out, and articulates both with the palatines and the pterygoids. The palatines are posteriorly flat and fenestrated. The maxillopalatines are thin plates which meet the anterior bifurcation of the vomer. The descending process of each lacrymal has a large foramen, the presence of which led R. O. CUNNINGHAM to distinguish Rh. Darwini from Rh. americana, where the foramen is simply a notch. GADOW, however, showed that the question of notch or foramen is simply individual variability, and I am in a position to assert the same of Rh. macrorhyncha. The existence of a complete descending process of the nasal has been denied. PARKER, however, has figured an ascending pillar of bone from the maxillary, and in a specimen of Rh. macrorhyncha this was joined by a suture to the anterior margin of the lacrymal. It has, it is true, no connection with the premaxillary part of the nasal; but this can scarcely interfere with a comparison of the

On the Tracheal Pouch of the Emu,' P. Z. S. 1867, p. 405.

2 For the lungs and air sacs of Struthiones see ante, p. 495. Those of Rhea have been described by W. N. PARKER, 'Note on the Respiratory Organs of Rhea,' P. Z. S. 1883, p. 141; of Dromæus by MALM, Om Luftrör-säcken,' &c., Öfv. K. Vet. Ak. Förh. 1880, p. 33.

6

3 PANDER and D'ALTON, Die Skelete der straussartigen Vögel. Bonn, 1827.

bone to the outer part of a nasal and to the naso-maxillary of the Dinornithidae (see below).

There is a well-developed, though thin and curved, ectethmoid lamina, which joins the maxillo-palatine below and the descending process of the lacrymal above. This has been also stated to be absent.

Rhea has seventeen cervical vertebra. The atlas is notched, as in Struthio, but not so widely. In the shoulder girdle the procoracoid is short, but is continued down to the articulations of the coracoid by the membrana coracoidea, of which, in a specimen of Rhea macrorhyncha before me, a

FIG. 242.-STERNUM OF Rhea (AFTER MIVART).

CC, coracoid grooves; ca, anterior lateral process; f, keel (?): lx, posterior lateral process.

portion is ossified as a thin spicule of bone shutting in the foramen coracoideum. The sternum (see fig. 242) has a median ventral prominence and two lateral thin rings of the bone, which may be indications of foramina. Three (sometimes four) pairs of ribs reach the sternum. The pelvis (fig. 243) has a small pectineal process. The pubes join the ischia posteriorly, and anteriorly an interobturator process, of which there are faint indications in Struthio, unite the two bones. Posteriorly the ilia are attached to the

ischia.

The structure of the skull of the emu' is not widely different from that of the skull of Rhea. The vomer is widely bifurcate behind, where it articulates both with pterygoids and palatines. The basipterygoids articulate with the pterygoids at the extreme posterior end of the

FIG. 243. PELVIS OF Rhea (AFTER MIVART).

il, ilium; lp, pectineal process; at, antitrochanteric process; st, supratrochanteric process; ps, interobturator process; i, ischium; p, pubis.

latter, instead of nearly halfway along them, as in other birds. The maxillo-palatines are hollow swollen plates, which unite with the vomer and premaxillaries, but come apart in the dried skull. The descending process of the lacrymal has a foramen, as in Rhea. It joins the thin lamina of the ectethmoid. The descending process of the

1 W. K. PARKER, On the Structure and Development of the Skull in the Ostrich Tribe,' Phil. Trans. 1868, p. 113.

L L

nasal is only represented in the specimen before me by a minute pointed bit of bone attached above to a point corresponding to that whence the 'naso-maxillary' arises in Rhea.

Dromaus has twenty cervical vertebra. The atlas is

FIG. 244.-SKULL OF EMU (AFTER HUXLEY).

Pmx, premaxilla; Map, maxillo-palatine; Vo, vomer; Pl, palatine; Pt, pterygoid;
*, basipterygoid process.

notched, very nearly perforated (fig. 66, p. 118). The procoracoid is not quite so well developed as in Rhea, but there are a pair of rudimentary clavicles.

The sternum (fig. 74, p. 129) much resembles that of Rhea; it is not notched and is rather pointed at its extremity. Three or four ribs reach it.

The pelvis (fig. 245) has the pubes and ischia quite free posteriorly in the dry skeleton; but they are united by cartilage, as in the latter with the ilium. The interobturator process is present, and shuts off an anterior portion of the obturator foramen.

The skull of Casuarius1 is very like that of Dromaus.

The number of cervical verterbræ in Casuarius varies from eighteen to nineteen. In the atlas the indication of the

closing of the notch for the odontoid process may be completed, as is shown in the cut (fig. 68, p. 118). The shoulder girdle is very like that of the emu, possessing also rudimentary clavicles. The membrana coracoidea may, however, be ossified, and there are two foramina. One of these lies between the membrana coracoidea and the coracoid, and is therefore apparently the homologue of the foramen in

W. H. FLOWER, 'On the Skeleton of the Australian Cassowary,' P. Z. S. 1871, p. 32.