60 On the Nature of ^^HcpmapopJiysesy 



XVI. — On the Nature of " Hcemapophyses ^'' in reply to some 

 Criticisms of M. Dollo. By G. A. Boulexger. 



In two papers published in the ' Bulletin scientifique de 

 France/ xxiv. 1892, of which extracts have been kindly sent 

 me by the author, M. L. Dollo has endeavoured to show 

 that his maxim, " Chez tons les vertebras, les cotes sont horao- 

 logues aux cotes et les hajmapophyses aux htemapopliyses," 

 being true, the views I have expressed as to the nature of the 

 Reptilian chevrons are necessarily incorrect. I fear my friend 

 lets himself be carried astray by theories which, however 

 fascinating they may appear when treated in the talented 

 manner with which all readers of his works are familiar, are, 

 in this special case, unsupported by facts. I maintain that 

 there is not at present the slightest evidence that the chevrons 

 are homologous throughout the Yertebrata, as my critic will 

 have it. An examination of the vertebral column of Am,ia 

 suffices to show how, in that type, the true ribs gradually 

 converge ventrally towards the caudal region, and do duty 

 for the " hgemapophyses." The embryological researches of 

 C. Scheel (Morphol. Jahrb. xx. 189£{, p. 1) also prove that in 

 the Teleostei the hiemapophyses are formed by the parapo- 

 physes or parapophyses and ribs. It further appears to me 

 that M. Dollo, when writing on the subject, had not present 

 to his mind the multitudinous moditications of the vertebral 

 column of Teleosteans, for I cannot see how his account of 

 the relations of the ribs and haemal arch can be reconciled 

 with the structure of such a well-known type as the typical 

 Scomberoids, Mackerel or Tunny. 



I here quote Cuvier on the Mackerel : — " L'dpine a trente 



et une vertebres, Les apophyses transverses torment 



I'anneau [haeraapophysis] des la dixifeme. Elles ont d'abord 

 deux cotes de chaque cote, partant du m^me point ; ensuite 

 les cotes se s^parent un peu. Les sup^rieures, plus courtes, 

 durent jusqu'a la dix-huiti^me vertebre ; les autres, plus 

 longues, cesseut des la treizieme." Hence we have on one 

 and the same vertebra (10th to 13th) the two ribs, assumed 

 by M. Dollo to represent the true rib and the hgemapophysis, 

 in addition to the heemal arch. 



A further argument against M. Dollo's theory of the 

 homology of the haemal arch throughout the Vertebrata is 

 derived from the fact that in certain Cyprinoids the anterior 

 thoracic vertebrte possess a ventral arch enclosing the aorta. 

 This arch is pronounced by Scheel to be formed by mere 

 fibrous processes of the centrum, and to be homologous with 

 the chevrons of Urodele Batrachians. 



