The/at bronchus/nn and/cc pulmonary/jj artery/nn in/in this/dt lung/nn type/nn maintain/vb a/at close/jj relationship/nn throughout/rb ./.
The/at pulmonary/jj vein/nn ,/, however/rb ,/, without/in the/at limiting/vbg supportive/jj tissue/nn septa/nns as/cs in/in type/nn 1/cd ,/, ,/, follows/vbz a/at more/ql direct/jj path/nn to/in the/at hilum/nn and/cc does/doz not/* maintain/vb this/dt close/jj relationship/nn (/( figs./nns 8/cd ,/, 22/cd )/) ./.
Another/dt marked/vbn difference/nn is/bez noted/vbn here/rb ./.
The/at pulmonary/jj artery/nn ,/, in/in addition/nn to/in supplying/vbg the/at distal/jj portion/nn of/in the/at respiratory/jj bronchiole/nn ,/, the/at alveolar/jj duct/nn ,/, and/cc the/at alveoli/nns ,/, continues/vbz on/rp and/cc directly/rb supplies/vbz the/at thin/jj pleura/nn (/( fig./nn 8/cd )/) ./.
The/at bronchial/jj artery/nn ,/, except/in for/in a/at small/jj number/nn of/in short/jj branches/nns in/in the/at hilum/nn ,/, contributes/vbz none/pn of/in the/at pleural/jj blood/nn supply/nn ./.
It/pps does/doz ,/, as/cs in/in type/nn 1/cd ,/, ,/, supply/vb the/at hilar/jj lymph/nn nodes/nns ,/, the/at pulmonary/jj artery/nn ,/, the/at pulmonary/jj vein/nn ,/, the/at bronchi/nns ,/, and/cc the/at bronchioles/nns --/-- terminating/vbg in/in a/at common/jj capillary/nn bed/nn with/in the/at pulmonary/jj artery/nn at/in the/at level/nn of/in the/at respiratory/jj bronchiole/nn ./.
No/at bronchial/jj artery-pulmonary/nn artery/nn anastomoses/nns were/bed noted/vbn in/in this/dt group/nn ./.


	Lung/nn type/nn 3/cd (/( (/( fig./nn 3/cd )/) is/bez to/in some/dti degree/nn a/at composite/nn of/in types/nns 1/cd ,/, and/cc 2/cd ./.
It/pps is/bez characterized/vbn by/in the/at presence/nn of/in incompletely/rb developed/vbn secondary/jj lobules/nns ;/. ;/.
well/rb defined/vbn ,/, but/cc haphazardly/rb arranged/vbn ,/, interlobular/jj septa/nns and/cc a/at thick/jj ,/, remarkably/rb vascular/jj pleura/nn (/( fig./nn 9/cd )/) ./.
The/at most/ql distal/jj airways/nns are/ber similar/jj to/in those/dts found/vbn in/in type/nn 1/cd ,/, ,/, being/beg composed/vbn of/in numerous/jj ,/, apparently/rb true/jj terminal/jj bronchioles/nns and/cc occasional/jj ,/, poorly/rb developed/vbn respiratory/jj bronchioles/nns (/( figs./nns 14/cd ,/, 15/cd )/) ./.
In/in this/dt instance/nn ,/, because/rb of/in incomplete/jj septation/nn ,/, the/at secondary/jj lobule/nn does/doz not/* constitute/vb in/in itself/ppl what/wdt appears/vbz to/to be/be a/at small/jj individual/jj lung/nn as/cs in/in type/nn 1/cd ./.
Air-drifts/nns from/in one/cd area/nn to/in another/dt are/ber ,/, therefore/rb ,/, conceivable/jj ./.
Distally/rb the/at bronchus/nn is/bez situated/vbn between/in a/at pulmonary/jj artery/nn on/in one/cd side/nn and/cc a/at pulmonary/jj vein/nn on/in the/at other/ap ,/, as/cs in/in type/nn 1/cd (/( (/( fig./nn 24/cd )/) ./.
This/dt relationship/nn ,/, however/rb ,/, is/bez not/* maintained/vbn centrally/rb ./.
Here/rb the/at pulmonary/jj vein/nn ,/, as/cs in/in type/nn 2/cd ,/, ,/, is/bez noted/vbn to/to draw/vb away/rb from/in the/at bronchus/nn ,/, and/cc to/to follow/vb a/at more/ql direct/jj ,/, independent/jj course/nn to/in the/at hilum/nn (/( figs./nns 23/cd ,/, 24/cd )/) ./.
The/at bronchial/jj artery/nn in/in its/pp$ course/nn and/cc distribution/nn differs/vbz somewhat/rb from/in that/dt found/vbn in/in other/ap mammals/nns ./.
As/cs seen/vbn in/in types/nns 1/cd ,/, and/cc 2/cd ,/, ,/, it/pps supplies/vbz the/at hilar/jj lymph/nn nodes/nns ,/, vasa/nn vasorum/nn to/in the/at pulmonary/jj artery/nn and/cc vein/nn ,/, the/at bronchi/nns and/cc the/at terminal/jj bronchioles/nns ./.
As/cs in/in type/nn 1/cd ,/, ,/, it/pps provides/vbz arterial/jj blood/nn to/in the/at interlobular/jj septa/nns ,/, and/cc an/at extremely/ql rich/jj anastomotic/jj pleural/jj supply/nn is/bez seen/vbn (/( figs./nns 9/cd ,/, 10/cd )/) ./.
This/dt pleural/jj supply/nn is/bez derived/vbn both/abx from/in hilar/jj and/cc interlobular/jj bronchial/jj artery/nn branches/nns ./.
Such/abl a/at dual/jj derivation/nn was/bedz strikingly/rb demonstrated/vbn during/in the/at injection/nn process/nn where/wrb initial/jj filling/vbg would/md be/be noted/vbn to/to occur/vb in/in several/ap isolated/vbn pleural/jj vessels/nns at/in once/rb ./.
Some/dti of/in these/dts were/bed obviously/rb filling/vbg from/in interlobular/jj branches/nns of/in the/at bronchial/jj arteries/nns while/cs others/nns were/bed filling/vbg from/in direct/jj hilar/jj branches/nns following/vbg along/in the/at pleural/jj surface/nn ./.
With/in completion/nn of/in filling/vbg ,/, net-like/jj anastomoses/nns were/bed noted/vbn to/to be/be present/jj between/in these/dts separately/rb derived/vbn branches/nns ./.
An/at unusual/jj increase/nn in/in the/at number/nn of/in bronchial/jj arteries/nns present/rb within/in the/at substance/nn of/in the/at lung/nn was/bedz noted/vbn ./.
This/dt was/bedz accounted/vbn for/in primarily/rb by/in the/at presence/nn of/in a/at bronchial/jj artery/nn closely/rb following/vbg the/at pulmonary/jj artery/nn ./.
The/at diameter/nn of/in this/dt bronchial/jj artery/nn was/bedz much/ql too/ql large/jj for/in it/ppo to/to be/be a/at mere/jj vasa/nn vasorum/nn (/( figs./nns 16/cd ,/, 23/cd ,/, 24/cd )/) ./.
In/in distal/jj regions/nns its/pp$ diameter/nn would/md be/be one-fourth/nn to/in one-fifth/nn that/dt of/in the/at pulmonary/jj artery/nn ./.
This/dt vessel/nn could/md be/be followed/vbn to/in the/at parenchyma/nn where/wrb it/pps directly/rb provided/vbd bronchial/jj arterial/jj blood/nn to/in the/at alveolar/jj capillary/nn bed/nn (/( figs./nns 17/cd ,/, 18/cd )/) ./.
Also/rb three/cd other/ap direct/jj pathways/nns of/in alveolar/jj bronchial/jj arterial/jj supply/nn were/bed noted/vbn :/: via/in the/at pleura/nn ;/. ;/.
through/in the/at interlobular/jj septa/nns ;/. ;/.
and/cc along/in the/at terminal/jj bronchiole/nn (/( figs./nns 14/cd ,/, 17/cd ,/, 18/cd ,/, 19/cd )/) ./.
One/cd bronchial/jj arteriolar-pulmonary/jj arteriolar/jj anastomosis/nn was/bedz noted/vbn at/in the/at terminal/jj bronchiolar/jj level/nn (/( fig./nn 26/cd )/) ./.



Discussion/nn-hl 
It/pps is/bez evident/jj that/cs many/ap marked/vbn and/cc striking/jj differences/nns exist/vb between/in lungs/nns when/wrb an/at inter-species/jj comparison/nn is/bez made/vbn ./.
The/at significance/nn of/in these/dts differences/nns has/hvz not/* been/ben studied/vbn nor/cc has/hvz the/at existence/nn of/in corresponding/jj physiologic/jj differences/nns been/ben determined/vbn ./.
However/rb ,/, the/at dynamics/nns of/in airflow/nn ,/, from/in morphologic/jj considerations/nns alone/rb ,/, may/md conceivably/rb be/be different/jj in/in the/at monkey/nn than/cs in/in the/at horse/nn ./.
The/at volume/nn and/cc ,/, perhaps/rb ,/, even/rb the/at characteristics/nns of/in bronchial/jj arterial/jj blood/nn flow/nn might/md be/be different/jj in/in the/at dog/nn than/cs in/in the/at horse/nn ./.
Also/rb ,/, interlobular/jj air/nn drifts/nns may/md be/be all/abn but/in nonexistent/jj in/in the/at cow/nn ;/. ;/.
probably/rb occur/vb in/in the/at horse/nn much/rb as/cs in/in the/at human/jj being/nn ;/. ;/.
and/cc ,/, in/in contrast/nn ,/, are/ber present/jj to/in a/at relatively/ql immense/jj degree/nn on/in a/at segmental/jj basis/nn in/in the/at dog/nn where/wrb lobules/nns are/ber absent/jj (/( Van/np Allen/np and/cc Lindskog/np ,/, '31/cd )/) ./.
A/at reason/nn for/in such/ql wide/jj variation/nn in/in the/at pulmonary/jj morphology/nn is/bez entirely/rb lacking/vbg at/in present/nn ./.


	Within/in certain/ap wide/jj limits/nns anatomy/nn dictates/vbz function/nn and/cc ,/, if/cs one/pn is/bez permitted/vbn to/to speculate/vb ,/, potential/jj pathology/nn should/md be/be included/vbn in/in this/dt statement/nn as/ql well/rb ./.
For/in example/nn ,/, the/at marked/vbn susceptibility/nn of/in the/at monkey/nn to/in respiratory/jj infection/nn might/md be/be related/vbn to/in its/pp$ delicate/jj ,/, long/jj alveolar/jj ducts/nns and/cc short/jj ,/, large/jj bronchioles/nns situated/vbn within/in a/at parenchyma/nn entirely/rb lacking/vbg in/in protective/jj supportive/jj tissue/nn barriers/nns such/jj as/cs those/dts found/vbn in/in types/nns 1/cd ,/, and/cc 3/cd ./.
One/pn might/md also/rb wonder/vb if/cs monkeys/nns are/ber capable/jj of/in developing/vbg bronchiolitis/nn as/cs we/ppss know/vb it/ppo in/in man/nn or/cc the/at horse/nn ./.
In/in addition/nn ,/, it/pps would/md be/be difficult/jj to/to imagine/vb chronic/jj generalized/vbn emphysema/nn occurring/vbg in/in a/at cow/nn ,/, considering/in its/pp$ marked/vbn lobular/jj development/nn but/cc ,/, conversely/rb ,/, not/* difficult/jj to/to imagine/vb this/dt occurring/vbg in/in the/at horse/nn or/cc the/at dog/nn ./.


	Anatomically/rb ,/, the/at horse/nn lung/nn appears/vbz to/to be/be remarkably/rb like/jj that/dt of/in man/nn ,/, insofar/rb as/cs this/dt can/md be/be ascertained/vbn from/in comparison/nn of/in our/pp$ findings/nns in/in the/at horse/nn with/in those/dts of/in others/nns (/( Birnbaum/np ,/, '54/cd )/) in/in the/at human/jj being/nn ./.
The/at only/ap area/nn in/in which/wdt one/pn might/md find/vb major/jj disagreement/nn in/in this/dt matter/nn is/bez in/in regard/nn to/in the/at alveolar/jj distribution/nn of/in the/at bronchial/jj arteries/nns ./.
As/ql early/rb as/cs 1858/cd ,/, Le/np Fort/np claimed/vbd an/at alveolar/jj distribution/nn of/in the/at bronchial/jj arteries/nns in/in human/jj beings/nns ./.
In/in 1951/cd ,/, this/dt was/bedz reaffirmed/vbn by/in Cudkowicz/np ./.
The/at opposition/nn to/in this/dt point/nn of/in view/nn has/hvz its/pp$ staunchest/jjt support/nn in/in the/at work/nn of/in Miller/np (/( '50/cd )/) ./.
Apparently/rb ,/, however/rb ,/, Miller/np has/hvz relied/vbn heavily/rb on/in the/at anatomy/nn in/in dogs/nns and/cc cats/nns ,/, and/cc he/pps has/hvz been/ben criticized/vbn for/in using/vbg pathologic/jj human/jj material/nn in/in his/pp$ normal/jj study/nn (/( Loosli/np ,/, '38/cd )/) ./.
Although/cs Miller/np noted/vbd in/in 1907/cd that/cs a/at difference/nn in/in the/at pleural/jj blood/nn supply/nn existed/vbd between/in animals/nns ,/, nowhere/rb in/in his/pp$ published/vbn works/nns is/bez it/pps found/vbn that/cs he/pps did/dod a/at comparative/jj study/nn of/in the/at intrapulmonary/jj features/nns of/in various/jj mammalian/jj lungs/nns other/ap than/cs in/in the/at dog/nn and/cc cat/nn (/( Miller/np ,/, '13/cd ;/. ;/.
'25/cd )/) ./.


	The/at meaning/nn of/in this/dt variation/nn in/in distribution/nn of/in the/at bronchial/jj artery/nn as/cs found/vbn in/in the/at horse/nn is/bez not/* clear/jj ./.
However/rb ,/, this/dt artery/nn is/bez known/vbn to/to be/be a/at nutrient/jj vessel/nn with/in a/at distribution/nn primarily/rb to/in the/at proximal/jj airways/nns and/cc supportive/jj tissues/nns of/in the/at lung/nn ./.
The/at alveoli/nns and/cc respiratory/jj bronchioles/nns are/ber primarily/rb diffusing/vbg tissues/nns ./.
Theoretically/rb ,/, they/ppss are/ber capable/jj of/in extracting/vbg their/pp$ required/vbn oxygen/nn either/dtx from/in the/at surrounding/vbg air/nn (/( Ghoreyeb/np and/cc Karsner/np ,/, '13/cd )/) or/cc from/in pulmonary/jj arterial/jj blood/nn (/( Comroe/np ,/, '58/cd )/) ./.
Therefore/rb ,/, an/at explanation/nn of/in this/dt alveolar/jj bronchial/jj artery/nn supply/nn might/md be/be the/at nutritive/jj requirement/nn of/in an/at increased/vbn amount/nn of/in supportive/jj tissue/nn ,/, not/* primarily/rb diffusing/vbg in/in nature/nn ,/, in/in the/at region/nn of/in the/at alveolus/nn ./.
If/cs this/dt be/be true/jj ,/, the/at possibility/nn exists/vbz that/cs an/at occlusive/jj lesion/nn of/in the/at bronchial/jj arteries/nns might/md cause/vb widespread/jj degeneration/nn of/in supportive/jj tissue/nn similar/jj to/in that/dt seen/vbn in/in generalized/vbn emphysema/nn ./.
One/pn would/md not/* expect/vb such/abl an/at event/nn to/to occur/vb in/in animals/nns possessing/vbg lungs/nns of/in types/nns 1/cd ,/, or/cc 2/cd ./.


	The/at presence/nn of/in normally/rb occurring/vbg bronchial/jj artery-pulmonary/jj artery/nn anastomoses/nns was/bedz first/rb noted/vbn in/in 1721/cd by/in Ruysch/np ,/, and/cc thereafter/rb by/in many/ap others/nns ./.
Nakamura/np (/( '58/cd )/) ,/, Verloop/np (/( '48/jj )/) ,/, Marchand/np ,/, Gilroy/np and/cc Watson/np (/( '50/cd )/) ,/, Von/np Hayek/np (/( '53/cd )/) ,/, and/cc Tobin/np (/( '52/cd )/) have/hv all/abn claimed/vbn their/pp$ normal/jj but/cc relatively/ql nonfunctional/jj existence/nn in/in the/at human/jj being/nn ./.
Miller/np (/( '50/cd )/) is/bez the/at principal/jjs antagonist/nn of/in this/dt viewpoint/nn ./.
In/in criticism/nn of/in the/at latter's/nn$ views/nns ,/, his/pp$ conclusions/nns were/bed based/vbn upon/in dog/nn lung/nn injection/nn studies/nns in/in which/wdt all/abn of/in the/at vascular/jj channels/nns were/bed first/rb filled/vbn with/in a/at solution/nn under/in pressure/nn and/cc then/rb were/bed injected/vbn with/in various/jj sized/jj colored/vbn particles/nns designed/vbn to/to stop/vb at/in the/at arteriolar/jj level/nn ./.
As/ql early/rb as/cs 1913/cd Ghoreyeb/np and/cc Karsner/np demonstrated/vbd with/in perfusion/nn studies/nns in/in dogs/nns that/cs bronchial/jj artery/nn flow/nn would/md remain/vb constant/jj at/in a/at certain/ap low/jj level/nn when/wrb pressure/nn was/bedz maintained/vbn in/in the/at pulmonary/jj artery/nn and/cc vein/nn ,/, but/cc that/cs increases/nns in/in bronchial/jj artery/nn flow/nn would/md occur/vb in/in response/nn to/in a/at relative/jj drop/nn in/in pulmonary/jj artery/nn pressure/nn ./.
Berry/np ,/, Brailsford/np and/cc Daly/np in/in 1931/cd and/cc Nakamura/np in/in 1958/cd reaffirmed/vbd this/dt ./.
Our/pp$ own/jj studies/nns in/in which/wdt bronchial/jj artery-pulmonary/jj artery/nn anastomoses/nns were/bed demonstrated/vbn ,/, were/bed accomplished/vbn by/in injecting/vbg the/at bronchial/jj artery/nn first/rb with/in no/at pressure/nn on/in the/at pulmonary/jj artery/nn or/cc vein/nn ,/, and/cc then/rb by/in injecting/vbg the/at pulmonary/jj artery/nn and/cc vein/nn afterwards/rb ./.
It/pps is/bez distinctly/rb possible/jj ,/, therefore/rb ,/, that/cs simultaneous/jj pressures/nns in/in all/abn three/cd vessels/nns would/md have/hv rendered/vbn the/at shunts/nns inoperable/jj and/cc hence/rb ,/, uninjectable/jj ./.
This/dt viewpoint/nn is/bez further/rbr supported/vbn by/in Verloop's/np$ (/( '48/cd )/) demonstration/nn of/in thickened/vbn bronchial/jj artery/nn and/cc arteriolar/jj muscular/jj coats/nns which/wdt are/ber capable/jj of/in acting/vbg as/cs valves/nns ./.
In/in other/ap words/nns ,/, the/at anastomoses/nns between/in the/at bronchial/jj artery/nn and/cc pulmonary/jj artery/nn should/md be/be considered/vbn as/cs functional/jj or/cc demand/nn shunts/nns ./.


	In/in addition/nn ,/, little/ap work/nn has/hvz been/ben done/vbn on/in a/at comparative/jj basis/nn in/in regard/nn to/in the/at normal/jj existence/nn of/in bronchial/jj artery-pulmonary/jj artery/nn anastomoses/nns ./.
Verloop/np (/( '48/cd ;/. ;/.
'49/cd )/) found/vbn these/dts shunts/nns in/in the/at human/jj being/nn but/cc was/bedz unable/jj to/to find/vb them/ppo in/in rats/nns ./.
Ellis/np ,/, Grindlay/np and/cc Edwards/np (/( '52/cd )/) also/rb were/bed unable/jj to/to find/vb them/ppo in/in rats/nns ./.
Nakamura/np (/( '58/cd )/) was/bedz unable/jj to/to demonstrate/vb their/pp$ existence/nn ,/, either/cc by/in anatomic/jj or/cc physiologic/jj methods/nns ,/, in/in dogs/nns ./.
The/at possibility/nn that/cs the/at absence/nn or/cc presence/nn of/in these/dts shunts/nns is/bez species-dependent/jj is/bez therefore/rb inferred/vbn ./.
Certainly/rb ,/, the/at mere/jj fact/nn of/in failing/vbg to/to demonstrate/vb them/ppo in/in one/cd or/cc another/dt species/nn does/doz not/* conclusively/rb deny/vb their/pp$ existence/nn in/in that/dt species/nn ./.
It/pps is/bez ,/, however/rb ,/, highly/ql suggestive/jj and/cc agrees/vbz well/rb with/in our/pp$ own/jj findings/nns in/in which/wdt we/ppss also/rb failed/vbd to/to demonstrate/vb normally/rb occurring/vbg bronchial/jj artery-pulmonary/jj artery/nn shunts/nns in/in certain/ap species/nns ,/, especially/rb the/at dog/nn ./.


	In/in conclusion/nn ,/, these/dts findings/nns suggest/vb the/at need/nn for/in a/at comparative/jj physiology/nn ,/, pathology/nn ,/, and/cc histology/nn of/in mammalian/jj lungs/nns ./.
In/in addition/nn ,/, a/at detailed/vbn interspecies/jj survey/nn of/in the/at incidence/nn of/in generalized/vbn pulmonary/jj emphysema/nn in/in mammals/nns would/md be/be interesting/jj and/cc pertinent/jj ./.
Also/rb ,/, for/in the/at present/nn ,/, great/jj caution/nn should/md be/be exercised/vbn in/in the/at choice/nn of/in an/at experimental/jj animal/nn for/in pulmonary/jj studies/nns if/cs they/ppss are/ber to/to be/be applied/vbn to/to man/vb ./.
This/dt is/bez especially/rb so/rb if/cs the/at dog/nn ,/, cat/nn or/cc monkey/nn are/ber to/to be/be used/vbn ,/, in/in view/nn of/in their/pp$ marked/vbn anatomical/jj differences/nns from/in man/nn ./.
Finally/rb ,/, it/pps is/bez suggested/vbn that/cs in/in many/ap respects/nns the/at horse/nn lung/nn may/md be/be anatomically/rb more/ql comparable/jj to/in that/dt of/in the/at human/jj than/cs any/dti other/ap presently/rb known/vbn species/nn ./.



Summary/nn-hl 
The/at main/jjs subgross/jj anatomical/jj features/nns of/in the/at lungs/nns of/in various/jj mammals/nns are/ber presented/vbn ./.
A/at tabulation/nn of/in these/dts features/nns permits/vbz the/at lungs/nns to/to be/be grouped/vbn into/in three/cd distinctive/jj subgross/jj types/nns ./.
Type/nn 1/cd ,/, is/bez represented/vbn by/in the/at cow/nn ,/, sheep/nn ,/, and/cc pig/nn ;/. ;/.
type/nn 2/cd ,/, ,/, by/in the/at dog/nn ,/, cat/nn ,/, and/cc monkey/nn ;/. ;/.
type/nn 3/cd ,/, ,/, by/in the/at horse/nn ./.
Lobularity/nn is/bez extremely/ql well/rb developed/vbn in/in type/nn 1/cd ;/. ;/.
absent/jj in/in type/nn 2/cd ;/. ;/.
imperfectly/rb developed/vbn in/in type/nn 3/cd ./.
The/at pleura/nn and/cc interlobular/jj septa/nns are/ber thick/jj in/in types/nns 1/cd and/cc 3/cd ./.
The/at pleura/nn is/bez extremely/ql thin/jj in/in type/nn 2/cd and/cc septa/nns are/ber absent/jj ./.
Arterial/jj supply/nn to/in the/at pleura/nn in/in types/nns 1/cd and/cc 3/cd is/bez provided/vbn by/in the/at bronchial/jj artery/nn ,/, and/cc in/in type/nn 2/cd ,/, by/in the/at pulmonary/jj artery/nn ./.
In/in types/nns 1/cd ,/, 2/cd and/cc 3/cd the/at bronchial/jj artery/nn terminates/vbz in/in a/at capillary/nn bed/nn shared/vbn in/in common/jj with/in the/at pulmonary/jj artery/nn at/in the/at level/nn of/in the/at distal/jj bronchiole/nn ./.
In/in type/nn 3/cd the/at bronchial/jj artery/nn also/rb provides/vbz blood/nn directly/rb to/in the/at alveolar/jj capillary/nn bed/nn ./.
True/jj terminal/jj bronchioles/nns comprise/vb the/at most/ql frequent/jj form/nn taken/vbn by/in the/at distal/jj airways/nns in/in types/nns 1/cd and/cc 3/cd ,/, although/cs small/jj numbers/nns of/in poorly/rb developed/vbn respiratory/jj bronchioles/nns are/ber present/rb ./.
Well/rb developed/vbn respiratory/jj bronchioles/nns ,/, on/in the/at other/ap hand/nn ,/, appear/vb to/to be/be the/at only/ap form/nn taken/vbn by/in the/at distal/jj airways/nns in/in type/nn 2/cd ./.
In/in type/nn 1/cd the/at pulmonary/jj vein/nn closely/rb follows/vbz the/at course/nn of/in the/at bronchus/nn and/cc the/at pulmonary/jj artery/nn from/in the/at periphery/nn to/in the/at hilum/nn ./.
This/dt may/md be/be due/jj to/in the/at heavy/jj interlobular/jj connective/jj tissue/nn barriers/nns present/rb ./.
In/in type/nn 3/cd ,/, this/dt general/jj relationship/nn is/bez maintained/vbn peripherally/rb but/cc not/* centrally/rb where/wrb the/at pulmonary/jj vein/nn follows/vbz a/at more/ql independent/jj path/nn to/in the/at hilum/nn as/cs is/bez the/at case/nn throughout/in the/at lung/nn in/in type/nn 2/cd ./.