1848 



HUMAN ANATOMY. 



dorsal branches, which are small and irregular. There are usually four large and well- 

 marked ventral secondary bronchi, besides one or two insignificant ones the nature 

 of which is not easily determined. The ventral bronchi describe a spiral course 

 through the lung, curving forward and inward as they descend, so as to be in the 

 main parallel with the chief fissure. The dorsal branches, running backward, inward, 

 and downward, are not more than four in number, and may be reduced to two. There 

 are two bronchial tubes besides those mentioned above : one, the apical brojiclnts, 

 supplies the upper part of the lung, on the right springing from the primary bronchus 

 2 cm. or less from its origin. It is a large branch, about 10 mm. in diameter, running 

 upward and outward, and divides into three branches, one of which ascends and two 

 of which run downward and outward on the front and back respectively. It is really 

 the first dorsal branch of the right primary bronchus, but we have not included it in 

 the dorsal branches. On the left the apical bronchus, which closely resembles the 

 right one, but is rather smaller, rises from the first ventral bronchus, of which it 

 may be called a dorsal branch. The other secondary bronchus, not included in the 

 foregoing scheme, is the subcardiac bronchus^ which on the right arises usually from 

 the main trunk between the first and second ventral bronchi, or from the second 



ventral bronchus. It 

 Fig. 1570. xnns, downward and 



inward to the region 

 in front of the hi- 

 lum and above the 

 lower border of the 

 lung, which may be 

 marked ofl as a sep- 

 arate lobe, held to 

 represent the cardiac 

 lobe of mammals. 

 On the left the cor- 

 responding bronchus 

 arises always from 

 the second ventral 

 branch. 



Homologies of the 

 Bronchi. — We are in- 

 debted to Aeby ' for the 

 idea, now practically 

 universally accepted, 

 that there is a main or 

 primary bronchus ex- 

 tending through the 

 lung and giving off both ventral and dorsal branches. After the bifurcation of the pulmonary 

 artery, each of its subdivisions reaches the front of the primary bronchus of each lung, and 

 (according to Aeby) crosses over it so as to lie behind it. This alleged crossing occurs on the 

 right just after the origin of the apical bronchus, which is said, therefore, to be above the cross- 

 ing, and is called by Aeby the epartcrial brojichus. Thus on the right all but one of the branches, 

 and on the left all, without exception, are given off below the crossing, and are called hyparterial 

 bronchi. Aeby attached so much importance to this relation that he considered the little irregu- 

 lar middle lobe of the right lung, because it is supplied by the first hyparterial bronchus, the 

 representative of the left upper lobe, the right upper lobe being without a mate and the two 

 lower lobes homologous. It is difficult to understand why such a relation should be of so great 

 import. Narath,^ in refutation of Aeby, pointed out that during fcetal life the pulmonary artery is 

 a very insignificant, and withal variable structure, and, moreover, that it does not cross fairly 

 over the main bronchus, but runs on its outer side, the crossing occurring, if at all, deep in the 

 lung. Narath [.howed also that the so-called eparterial apical bronchus of the right lung is 

 present in the left, arising from the first ventral instead of the primary bronchus. It is a ter- 

 tiary bronchus from the first ventral which, especially on the right, is (among mammals) given 

 to wandering, so that it may spring from the main bronchus or even from the trachea. The 

 arterial relation he considers of no importance. Huntington,^ after much work on human 

 and mammalian lungs, came to somewhat similar conclusions. He believes that the primary 

 type among mammals is one with a hyparterial bronchus on both sides, and the furthest 



' Der Bronchialbaum der Saugethiere und des Menschen, 1S80. 



« Verhandl. d. Anat. Gesellschaft, 1892. 



' Annals of the New York Academy of Sciences, 1898. 



Relations of bronchial tree to posterior thoracic wall, as shown by X-rays. 



(After Blake.) 



