THE BESPIEATOItY APPARATUS IN BIRDS. 477 



and subdivide at tMs periphery, that they cover it with their ramifications, and do not 

 leave it to enter the pulmonary parenchyma until their volume has been considerably 

 reduced. 



" The conduits leaving the orifices situated on the inner wall of the ajrial trunk 

 ramify on the inferior face of the lung ; those proceeding from the echeloned orifices on 

 the outer wall are distributed on the opposite face. The first constitute the diaphrag- 

 matic, and the second the costal bronchial tubes. 



" The diaphragmatic bronchial tubes, four in number, like the orifices from which 

 they originate, may be distinguished by the numerical names of first, second, third, and 

 fourth, in proceeding from before to behind ; the first bronchus is carried forward 

 horizontally, the second transversely inwards, the third obliquely inwards and back- 

 wards, and the fourth directly backwards. In view of theii- divergent direction, which 

 resembles a fan, they might be desiguated as the anterior, internal, and posterior 

 diaphragmatic bronchial tubes ; and to distinguish the last tvro, the more voluminous 

 one, which is directed backwards and inwards, might be named the great posterior 

 diaphragmatic bronchus, and the one passing directly backwards the small posterior 

 diaphragmatic bronchus. 



" The cnstal bronchial tubes, seven in number, may be also desiguated as first, second, 

 third, etc., in proceeding from before to behind ; parallel at their origin, and in juxta^ 

 position, like the pipes of an organ, they separate after following a certain course, and 

 affect, by their divergence, the fan-shape already observed in the disposition of the 

 diaphragmatic bronchise. Like the latter, they become peripheral from their origin, and 

 spread out from centre to circumference. The fii'st is carried very obliquely upwards 

 and inwards, to attain the anterior extremity of the lung ; all the branches it furnishes 

 arise from its anterior wall, and those which are nearest its origin are inflected to gain 

 the external border of the organ ; the succeeding tubes are directed forwards, the others 

 forwards and inwards ; while all proceed to meet those coming from the anterior 

 diaphragmatic bronchus, though they do not anastomose with them. Coming in contact, 

 they plunge into the pulmonary tissue in such a way, that, when a lung is inflated, we 

 observe between these two orders of ramifications a very manifest groove, which is 

 perfectly distinct from those due to the protrusion of the ribs ; this groove evidently 

 represents, though in a rudimentary state, the interlobular fissures in the lungs of 

 quadrupeds. 



"The second, third, and fourth costal bronohise follow a transverse course, and 

 ramify on the inner border of the lung; the fifth and sixth incline towards the 

 posterior extremity of the organ ; the seventh, very small, reaches this extremity and 

 disappears. 



" The first costal bronchus is the most voluminous : those succeeding it gradually 

 diminish in calibre. At their point of emergence they adhere closely to the ribs; all are 

 imperforate, and this feature essentially distinguishes them from those occupying the 

 opposite face. 



" The canaliculi furnished by these principal tubes do not sensibly differ in calibre 

 in the various bronchi : all offer an equal diameter, and their dimensions are only in 

 relation to the total volume of the lung. All are detached at a right angle from the 

 pulmonary wall of each bronchus, and descend perpendicularly into the lung ; and all, 

 from their origin to their termination, preserve the same diameter, and consequently the 

 same cylindrical form. If this mode of ramification be compared with that observed 

 in Mammals, it will be seen to differ considerably. In the latter class, the air-passages 

 affect the dichotomous division proper to the arteries and veins, the result of which is a 

 series of arboreal canals decreasing in capacity. In birds only two kinds of conduits are 

 observed, the primitive and peripheral, disposed around a generating axis like the barbs 

 of a feather on their stalk ; and the secondary and parenchymatous, implanted on the 

 pulmonary walls of the first, like the hairs of a brush on their common base. These 

 two arrangements are evidently similar, except that tlie peripheral canals, which are few, 

 only form a single row on each side ; while the canaliculi, very numerous, form several. 

 Consequently, it may be said that the mode of ramification proper to Mammalia is essen- 

 tially dichotomous, and that observed in birds essentially penniform. 



" Independently of the canalicuh arising from the pulmonary walls of the diaphragm- 

 atic and costal bronchife, there are others which spring directly from the generative 

 trunk ; but in their dimensions, direction, form, and general disposition, they do not 

 differ from the preceding. 



" How do these canals terminate ? Notwithstanding the importance of this question, 

 it has been generally neglected ; though its solution alone may furnish the analogies and 

 differences necessary for the parallel which has always been attempted to be established 

 between the lungs of birds and those of other vertebrates. Our special researches on this 



