AG THE STRUCTURE OF MAN 
appear at first sight the more likely, from the fact that whereas 
in man an eparterial bronchus is present only on the right side, 
in some Mammals it occurs (either bronchial or tracheal in 
origin) on both right and left. 
But all these animals, as Gegenbaur has remarked, in the 
rest of their organisation do not by any means show primitive 
conditions which can be considered to bear on the genealogy of 
Man: and great care is therefore necessary in dealing with the 
question in hand. Cases, in Man, lke those described by Dalla 
Rosa and Bohls, in which an eparterial bronchus is present on 
both sides? must not therefore be hastily classed as atavistic. 
It is, further, a very remarkable fact that the Marsupials, 
Rodents, Insectivora, Lemuroidea, and Apes, show no sign of 
original bilateral symmetry of the lungs. Further, the ontogeny 
of Man throws no light on the subject. We therefore at present 
can neither decide along what line of descent the Mammals 
above referred to may have inherited their symmetrical eparterial 
bronchi, nor in what manner the existence of these is to be ex- 
plained. It is, however, certain that if the human lungs originally 
bore homologous superior lobes, this symmetry must have been 
early lost. In face of these facts it 1s idle to speculate as to 
probable causes which may perchance have effected a gradual loss 
of symmetry of the bronchi. 
1 Eg. Bradypus, Equus, Elephas, Phoca, Phoceena communis, Delphinus delphis, 
and Auchenia. 
2 The presence on both sides of an eparterial bronchus has only twice been 
observed in Man—once where the viscera were in the normal position, and once in a 
case of situs inversus. In both instances there were also marked anomalies of the 
trunks of the larger arteries in the thorax. On each side three well-defined pulmonary 
lobes were found, and bilateral symmetry was complete (Dalla Rosa). 
Complete absence of the eparterial bronchus, and the existence of a tracheal near 
a bronchial eparterial bronchus, have been observed in Man. In the latter case, 
according to Chiari, it would appear that one of the collateral (dorsal) branches of 
the normal bronchial eparterial bronchus had become independent, and wandered 
up to the trachea. This view receives support from the well-known tendency 
of the lateral bronchus to give up branches to the principal, and from the 
study of cases in which two eparterial bronchi, one above the other, are found. 
The upper of these is evidently a branch of the ordinary eparterial bronchus 
shifted on to the main bronchus, and in this phenomenon we have an intermediate 
stage between the normal condition and that of the tracheal bronchus. The 
latter may therefore be regarded as a branch of the ordinary eparterial bronchus 
which has wandered farther up. I put forward these views with all reserve. 
[His has shown that in Man the first hyparterial bronchus of the left lung divides 
immediately after its origin, giving off an ascending branch (unrepresented on the 
right side) which runs forwards to the apex of the lung. Robinson has shown (Jowr. 
Anat. and Phys., vol. xxiii. p. 240) that the same is true of the Rat, and he suggests 
that this ascending branch may, as it were, compensate for the absence of a distinct 
eparterial bronchus. ] 
