564 PROF. HUXLEY ON THE RESPIRATORY [Juue 20, 



tions, which are in relation with the pulmonary parenchyma, are per- 

 forated by minute rounded apertures. These lead into canals which 

 are directed, at first, more or less at right angles to the surfaces of the 

 bronchia upon which they open, and pass, side by side, sometimes 

 anastomosing with one another, to some other bronchium than that 

 from which they start. They may be termed parabro7ichia ("canaux 

 tertiaires," Cuvier; "bronchial tubes," Rainey; "Lungenpfeifen" of 

 the Germans). The lumina of these canals are interrupted at pretty 

 regular intervals by transverse circular folds which contain unstriped 

 muscular fibres. The interspaces between these folds are more or 

 less subdivided by oblique or longitudinal folds of a similar nature 

 into foss(B ; and the walls of these fossae present smaller depressions 

 or fossulce, which directly, or indirectly, open into the intercapUlary 

 air-passages. These last occupy the meshes of the capillary network 

 into which the pulmonary vessels resolve themselves. 



This description (with possibly some variation in the number of 

 the ostia and air-sacs) applies to the respiratory apparatus of every 

 known bird, and to that of no other animal ; but it also applies, almost 

 word for word, to Apteryx. Hence there can be no doubt that the 

 respiratory organs of this bird are thoroughly and typically ornithic, 

 and that they present not the slightest approximation to those of the 

 Mammalia. 



If the organs of respiration of Apteryx are compared with those 

 of a carinate bird of similar size and form of trunk, such as a Duck, 

 the resemblances and differences between the two can be easily 

 traced. 



1. The Duck's lungs are considerably larger both absolutely and 

 relatively. 



2. The anterior ventral margin in the Duck is longer than the 

 posterior. The reverse obtains in Apteryx. 



3. The pulmonary aponeurosis of the Duck is very delicate ; in 

 Apteryx it is strong and thick. 



4. The median vertical septum in the Duck is much deeper, and 

 anteriorly it is supported by the long hypapophyses of the anterior 

 thoracic vertebrae. At the same time it is far less strongly fibrous 

 than the corresponding structure in Apteryx. The mesial attachment 

 of the pulmonary aponeurosis is to the ventral edge of the septum, 

 close to that of the oblique septum, in the Duck ; while in Apteryx 

 the two are separated by a considerable interval, throughout which 

 the thin and membranous part of the dorsal median septum divides 

 the mesial ends of the intermediate and posterior loculi from one 

 another. 



In the Duck, the median dorsal septum lies throughout between 

 the superior facets of the internal faces of the two lungs. In other 

 words, this superior facet is much deeper in the Duck than in 

 Apteryx. 



5. The oblique septum is extremely thin and weak in the Duck ; 

 while in Apteryx it is a very strong aponeurotic membrane, with 

 interlacing fibres diverging from two tendons attached to the under 

 face of the posterior thoracic vertebrae. In the Duck it contains, on 



