OCR Text |
Show 564 PROF. HUXLEY ON THE RESPIRATORY [June 20, tions, which are in relation with the pulmonary parenchyma, are perforated 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 termedparabronchia ("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 fossa ; and the walls of these fossae present smaller depressions or fossula, which directly, or indirectly, open into the intercapillary 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 |