TIIK /,7.> /7/M 7V >/,T l/'/M/,M7V> /.V /;//;/<X. 477 



'iMiviiii- at tliis |*-riphery, that they coyer it with their ramifications, ami do not 

 l.-i\e it to enter tli.' pulmonary parenchyma until their volume ha-s l>ei n coiiM.l. rably 

 rcdr. 



! conduits leaving the orifices situated on the inner wall of thn rorial trunk 

 minify on the interior la. 1 .' of the lung; those proceedim,' from the echeloned orifices on 

 tin- outer wall ue distributed on the o] 4* .site lace. The first constitute the diaphrag- 

 matic. and the >. ., ,n,i th.- costal bronchial tubes. 



" The tlinjiltnti lui'itic lironchial tuttes, 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 Defore to In-hind; the tirst bronchus is < arried forward 

 hori/ontally. the second transversely inwards, the third obliquely inwards and back- 

 wanls. and the fourth directly backwards. In view of their divergent direction, which 



les a fan, they miirht be de-i^nated as the- anterior, internal, and p> 

 diaphragmatic bronchial tubes; and to distinguish the last two. the more voluminous 

 i>ne, which is directed Imckwards and inwards, might be named the great posterior 

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

 diaphragmatic bronchus. 



The <-..xf<i/ Immrliinl tubes, seven in number, may be ulso designated as first, second. 

 third, et' 1 .. in proceeding from before to behind; parallel at their origin, and in juxta- 

 I>osition. like the pipes of an organ, they separate after following a certain course, and 

 utfe.-t, by tluir divergence, (he fun-shape already observed in the disposition of the 

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

 spread out from centre to circumference. The first is carried very obliquely upwards 

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

 lerior wall, and those which are nearest its origin are inflected to gain 

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

 forwards and inwards; while all proceed to meet those coining 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 

 :ly 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 

 quadmp. ds. 



The second, third, and fourth costal bronchiae follow a transverse course, and 

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

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

 di sap] tears. 



i 'ic tirst costal bronchus is the most voluminous: those succeeding it gradually 

 dimini.-h in calibre. At their point of emergence they adhere closely to the ribs; all an- 

 iiiilcifor.it -, and this feature essentially distinguishes them from those occupying the 



op|N>site I i 



Tin- ''innlii'iili t'nrni-hed by these principal tubes do not sensibly ditler in calibre 

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

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

 pulmonary wall of each bronchus, and defend ]K-r]M-ndicularly into the IIIIILT; and all, 

 from their origin to their terminaton, preserve the same diameter, and consequently tin- 

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

 in Mniiiinals. it will IK; wen to differ considerably. In tin- latter cbiss, the air-passages 

 affect the dichotomous division proper to the aiteiies and veins, the n .-nit of which is a 

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

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

 of a feather on their stalk; and the secondary and parenchymatoiis, imp hinted on the 

 pulmonary walls of the first, like the hairs of a b,u.-h on th.ir i-.immon base. The*.- 

 two arrangements an- esideiitly similar, except thattlie |>eiipheral canals, which are few. 

 only f..rm n single row on each side ; while the canaliculi, very numeron-. form .-. 

 ('on-e.|iiently, it may be said that the mode of ramiticat : on proper t Mammalia is eaMQ- 

 lially dichot-mi'iis. and that observed in birds es.-entially ix-nniform. 



" independently of the canuliculi arising from the pulmonary walls of the diaphragm- 

 atic and c,,-tal hr.nichiie. there ar. others which spring directl) from tin 

 trunk; but in tin ir dimensions, direction, form, and general d .,, not 



differ from the preceding. 



How do these canals terminate '> Notwithstanding the ini|>ortaniv of this | 

 it has been generally n.^iect. d ; thoii-h fts solution alone may furni-h the analogi. 

 differences necessary for the parallel which has alway- I n attempt. .1 to be establish. <1 

 .n the lung's of birds and iho*- uf oth. r vertebrates. Our special rusearoheson thi- 



