294 PROF. OWEN ON THE ANATOMY 
than in other birds ; its antero-posterior diameter is three lines ; its transverse diameter 
four lines. The cornea transparens is very convex, and two lines in diameter. The 
sclerotic is thin, but the margin supporting the cornea is strengthened by a circle of small 
osseous plates. The choroid is a delicate membrane; its pigment is of a light brown 
colour. The ciliary processes commence at the ciliary ring, each process having at its 
origin a slight linear rising, which becomes gradually wavy and tortuous as it approaches 
the lens, anterior to the circumference of which it projects freely to a small extent. 
The iris in the specimen examined was one-third of a line in breadth. The optic nerve 
terminates by a small round aperture. The lens is two lines in breadth, and nearly 
one line at the thickest part, being thus more convex than in other birds. The ex- 
ternal appendages of the eye presented no peculiarities, except the very great strength 
of the orbicularis palpebrarum ; the membrana nictitans had the usual trochlear muscles : 
its free margin was black. 
The singularly long and narrow nasal passages are closed and defended externally by 
the inflected outer margins of the nasal and upper process of the long intermaxillary 
bones. The relative extent and complexity of the turbinated bones, and the capacity 
of the posterior part of the nasal cavity exceed those of any other bird; and the sense 
of smell must be proportionally acute and important in the economy of the Apteryz. 
Concluding Observations. 
On a review of the preceding details of the organization of the Apteryz, it will be 
seen that, commencing with the skeleton, all the leading modifications of that basis of 
its structure connect it closely with the Struthious group. In the diminutive and 
keel-less sternum it agrees with all the known Struthious species, and with these alone. 
The two posterior emarginations which we observe in the séernum of the Ostrich are 
present in a still greater degree in the Apteryx ; but the feeble development of the ante- 
rior extremities, to the muscles of which the sternum is mainly subservient as a basis of 
attachment, is the condition of a peculiarly incomplete state of the ossification of that 
bone of the Apteryx ; and the two subcircular perforations which intervene between the 
origins of the pectoral muscle on the one side, and those of a large inferior dermo- 
cervical muscle on the other, form one of several unique structures in the anatomy of 
this bird. We have again the Struthious characters repeated in the atrophy of the 
bones of the wing, and the absence of the clavicles, as in the Rhea’. Like testimony 
is borne by the expansively developed iliac and sacral bones, by the broad ischiwm and 
slender pubis, and by the long and narrow form of the pelvis. We begin to observe a 
1 In the Ostrich the clavicles are undoubtedly present though anchylosed with the scapula and coracoids, 
and separate from each other. In the Cassowary and Emeu they exist as separate short styliform bones. 
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