276 PROF. OWEN ON THE ANATOMY 
In the extreme case of the raptorial bird above-quoted, the advantage of such an 
arrangement appears sufficiently obvious to justify tne teleological hypothesis here pro- 
posed ; and in the rest of the class the like benefit may result from this arrangement of 
the renal veins to a degree corresponding with the necessity for it which may exist. 
In the Apteryz the great renal vein (s, Pl. L.) is not imbedded in the substance, but is 
continued along the anterior or under-surface of the kidney, receiving the blood from 
the lobules of the gland by many oblique but wide openings ; the venous trunks of the 
two kidneys anastomose, as in other birds, posteriorly, to form the commencement of 
the mesenteric vein (¢, Pl. L.) ; and, anteriorly, after receiving the iliac veins, they unite 
to form the vena cava, and thus complete the great circulus venosus renalis. ‘The modi- 
fications of this part of the venous system were less important than I had been led 
to anticipate in a bird whose comparatively limited powers of locomotion must be at- 
tended with less partial and excessive action of the respiratory system than in birds of 
flight. 
The organs of respiration in birds are so eminently characteristic of that class, and 
so obviously framed with especial reference to the faculty of aerial progression, that 
in the Apterye—a bird of nocturnal and burrowing babits, and of which the wings 
are reduced to the most rudimental condition,—the examination of the associated 
modifications of the respiratory system promised to be replete with peculiar in- 
terest. It was, in fact, the first point to which I directed my attention, and having 
made a preparatory inflation of the pulmonary organs by the trachea, I proceeded to 
open the abdomen, and displaced the viscera with great care ; but, as has been already 
stated, there was not any trace of the extension of air-cells in the interspaces of the ab- 
dominal viscera ; and the whole of them having been removed, I was not less gratified 
than surprised to find a complete and well-developed diaphragm separating the abdo- 
minal from the respiratory cavity. This septum did not present any large openings 
corresponding to those by which the air is continued into the abdomen in the other Stru- 
thious birds, but was here perforated only for the transmission of the w@sophagus and 
large blood-vessels. 
The diaphragm of the Apteryz differs from that which characterizes the class Mammaha 
in the following points; first, in the greater relative extent of the anterior or post- 
sternal interspace ; secondly, in the greater proportion of tendinous or aponeurotic tissue 
which enters into its composition ; thirdly, in being perforated by three different large 
arteries, and not by the vena cava or splanchnic nerves ; and lastly, in the different rela- 
tive positions of the cesophageal and aortic openings. The plane of the diaphragm is 
more horizontal, or rather more parallel with the axis of the trunk, than in the Mam- 
malia generally ; but some of the aquatic species, as the Dugong, present a position of 
the diaphragm almost similar to that of the Apteryz. 
The origins of the vertebral or lumbar portion of the diaphragm are by two well- 
developed crura (Pl. LII. «, fig. 1.), which are attached to slight prominences on the 
