THE LUNGS. 1849 



departure from it one with symmetrical eparterial bronchi. The type found in man is the most 

 common among mammals. Huntingdon would do away entirely with the terms "eparterial" 

 and " hyparterial," except for purposes of topography. Certainly there is no need of them in 

 human anatomy as a special study ; whether or not the arterial relations should, as Narath main- 

 tains, be absolutely discarded in comparative anatomy, we must leave undetermined. 1 



It must be admitted that were our knowledge derived solely from the human lung it would 

 be impossible to make out this plan. We shall now describe what is actually to be seen. 



Distribution of the Bronchi. In the right lung the apical bronchus, with a diameter of 

 about 10 mm., arises about 2 cm. from the trachea (often nearer and rarely farther), and, 

 entering the top of the hilum, divides as described above. The diameter of the main trunk, after 

 giving off the apical branch, is 12 mm. The first right ventral branch arises from its outer side, 

 about 5 or 6 cm. from the bifurcation of the trachea, and runs downward, outward, and for- 

 ward. It is about 8 mm. in diameter. The apical branch and the first ventral supply the supe- 

 rior lobe, of which the middle lobe is really a part. Shortly after the origin of the first ventral 

 branch the chief bronchus seems to break up into a bundle of branches running mostly in the 

 same general direction, but diverging. It is usually not possible to determine which is the 

 main trunk, but the subcardiac branch may sometimes be distinguished. In the left hmg the 

 first branch is the first ventral, with a diameter of 12 mm., arising some 40 mm. from the bifurca- 

 tion. It gives off the apical, 7 or 8 mm. in diameter, after which the diameter of the main 

 branch is 12 mm. It presently breaks up like the right one. On this side the first ventral sup- 

 plies the upper lobe. A branch from the second ventral goes to the accessory lobe, if there 

 be one. The branches of the left bronchus are very apt to give the appearance of being divided 

 into an upper and a lower set, the former, consisting of the first ventral branch, bearing the 

 apical and supplying the superior lobe, while the lower sheaf of branches supplies the inferior. 



The secondary bronchi give off branches of 4 or 5 mm. in diameter, which diverge at acute 

 angles from the parent trunk, and in turn give off smaller branches at continually greater angles. 

 The branches to the lobules are probably the fourth or fifth branches. They are about i mm. 

 in diameter and arise by the subdivision of the preceding branch. In the larger tubes the 

 ramification is clearly from the side, but in the smaller ones it is more suggestive of a splitting. 

 His, 2 Minot. 3 and more recently Justesen 4 defend the theory that the origin of the bronchi is 

 throughout by bifurcation, with subsequent unequal growth of the subdivisions until we come to 

 the smallest. Aeby gives the following table of diameters of the main bronchus above the origin 

 of the chief branches, the nomenclature being his. 



Right. Left. 



Above the eparterial branch 12.8 mm. . . . 



Above the first hyparterial branch 9.6mm. 10.1 mm. 



Above the second hyparterial branch 7.2mm. 7.7mm. 



Above the third hyparterial branch 5.8 mm. 6.4 mm. 



Above the fourth hyparterial branch 4.6 mm. 5.3 mm. 



The variations of the bronchial tree are very numerous. Very rarely indeed the right 

 apical branch does not spring from the primary bronchus, so that the disposition of the two 

 sides is symmetrical. The origin of the left apical from the primary bronchus has been 

 observed in two or three cases of infants, which also makes the arrangement symmetrical. 

 Chiari 5 has seen several cases in which the right apical bronchus is double, the duplication 

 being apparently due to the springing of one of its branches from the main bronchus. The 

 right apical bronchus may spring from the trachea, as in the sheep and other mammals. We 

 have such an instance in which it is separated from the chief bronchus by the azygos vein. 

 The dorsal secondary bronchi are particularly likely to be reduced in number. The ventral 

 ones may also be reduced by two having a common origin or by one becoming merely the 

 branch of another. The number may be apparently increased by the separate origin from the 

 parent stem of what are normally branches of branches. 



The Lung Lobule. The surface of the lung- is covered with lines of con- 

 nective tissue containing blood-vessels and lymphatics, with pigment either within the 

 latter or free, the lines marking off little polygons (Fig. 1568), which are the bases of 

 pyramidal masses of pulmonary tissue known as the lobules. The shape of the latter 

 within the depths of the lungs is not accurately known ; those at the sharp borders 

 are modifications of the typical ones at the surface. The bases of the pyramids at 

 the surface are bounded by four, five, or six sides, the larger diameter varying from 

 10-25 mm - an d the smaller from 7-12 mm. If the base be assumed to be square, 

 the average breadth would be 12.57 mm- 6 The average height is 13 mm. The 

 lobules are separated from one another by a layer of connective tissue containing 



1 The latest and most elaborate work on this subject is Narath' s Der Bronchialbaum der 

 Saugethiere und des Menschen, Stuttgart, 1901. 

 1 Archiv f. Anat. u. Phys., Anat. Abth., 1887. 



3 Human Embryology, 1892. 



4 Archiv f. mikro. Anat., Bd. Ivi., 1900. 



5 Zeitschrift fiir Heilkunde, Prag., Bd. x., 1890. 



6 Bibliographic Anatomique, 1898. 



