176 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. 1 



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, like those described by Dalla 

 Kosa and Bohls, in which an eparterial bronchus is present on 

 both sides 2 must not therefore be hastily classed as atavistic. 



It is, further, a very remarkable fact that the Marsupials, 

 Eodents, 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 is idle to speculate as to 

 probable causes which may perchance have effected a gradual loss 

 of symmetry of the bronchi. 



1 E.g. Bradypus, Equus, Ulephas, Phoca, Phocceiia 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 (Jour. 

 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. ] 



