SUBJECT INDEX — MORPHOLOGICAL SECTION 



417 



For a scholarly presentation of the phylo- 

 genesis of limbs throughout the vertebrates, 

 from the data of comparative anatomy and 

 paleontology, see Ik-Gregory, W. K. 1915.1. 



EARLIER VIEWS 

 These are largely summarized in Mivart, St. 

 G. 1879.1 and are repeated in Cope, E. D. 1890.1. 



Limbs considered as diverging appendages 

 attached to ribs, with a shoulder-girdle of 

 axial origin. Owen, R. 1848.1. 



Limbs considered homologous with epi- 

 pleural spines, and external to visceral wall 

 of body. Goodsir, J. 1857.1. 



Vertical fins considered of bifold origin: 

 paired fins considered portions of lower azy- 

 gos fins prevented from uniting by inter- 

 posed body-cavity. Humphry, G. M. 



1870.1, 1871.1. 



Vertebrate limbs considered as modified 

 ribs by Maclise in Todd, R. B. " Encyclo- 

 paedia," 1832, vol. 4, p. 70, and fcyOken, 

 1843, " Lehrbuch der Natur-Philosophie, " 

 p. 330. 



View that preaxial {upper) border of 

 pectoral limb is homologous with the same 

 border of the pelvic limb. Wilder, B. G. 

 1872.1; Wyman, J. 1868.1. 



Opposite view of reversed homologies, i.e., 

 that preaxial border of pectoral is serially 

 homologous with ventral border of pelvics. 

 Braus, H. 1900.1 (p. 165). 



Miscellaneous or unclassified papers re- 

 lating to the origin of limbs. Eisler, P- 

 1895.1; GiU, T. N. 1898.2; Macdonald, 

 W. 1840.1, 1872.1; Mehnert, E. H. 



1897.1; DoUo, L. Add. 1896.1. 



Branchial or gill arch h3^othesis 



This hypothesis of Gegenbaur holds that 

 the paired fins have been derived from gill 

 structures, the gill-arch having been modi- 

 fied into the limb-girdle, and the fin itself 

 having been derived from the gjH-septum. 

 The position of the pelvic fins is attributed 

 to their backward migration. 



It considers a biserial appendage like 

 that of Ceratodus (the Archipterygium) 

 as the type from which all other fins and 

 legs have been derived by a shortening 

 of the axis and a loss of the pre-axial 

 radials. 



The principal papers in support of this 

 hypothesis are •Braus, H. 1899.2, 1900.1, 

 1906.1; Davidoff, M. 1879.1; Fur- 

 bringer, M. 1902.1, 1903.1; •Gegenbaur, 

 0. 1864.2, 1870.2,.4, 1873.1, 1876.1, 



1879.2, 1895.2; •Klaatsch, H. 1896.1. 

 Other papers of lesser importance are 



Bunge, A. 1874.1; Driiner, L. 1906.1; 

 Emery, C. 1887.2, 1897.3; Jaekel, O. 

 1899.3,.4; Zalenskii, V. V. 1898.1, .2. 



The chief points made against this hy- 

 pothesis by its opponents are summarized in 

 Goodrich, E. S. 1906.1, and in Osbum, 

 R. 0. 1907.2. 



Cell-accumulation hypothesis 



This view of Geddes, the most recent of 



all, " does not in reality oppose the lateral 



fin hypothesis. Rather it expands it in one 



. direction and refines it in another. It 



appears, too, to link together it and the 

 modified giU-arch hjpothesis." 



Briefly, it holds that in in-fry developing 

 vertebrate there are five cell regions which 

 are lines of potential cell-accumulation. 

 At points where three regions meet, the 

 tendenej' to cell-accumulation is especially 

 marked. There are four such points and 

 the cell-aceumulations formed around 

 them provided, far back in phylogeny, 

 material capable of being selected to 

 form the bases of new organs. At their- 

 commencement the limbs were, and still 

 are, altogether independent of the cepha- 

 lised axial part of the embryo, but later 

 passed under its dominance. 



For the full statement of this hypothesis, 

 see •Geddes, A. C. Add. 1912.1. 

 External-gill hypothesis 



This hypothesis of Kerr considers that 

 the external gills were potentially motor 

 and supporting structures and have given 

 rise to limbs. The Gegenbaur view of the 

 backward migration of the limbs is ac- 

 cepted together with his derivation of the 

 limb girdle. The necessity of a skeletal 

 axis in the external gill is provided for by 

 Budgett's description of a rod of cartilage 

 projecting into the external gill of the 

 larval Polypterus. 



For the original presentation of this view, 

 see Kerr, J. G. 1900.2, 1901.2. 



It has been further elaborated in -kProf. 

 Kerr's " Text-book of Embryology," 

 1919, vol. 2, pp. 449-453. 



Lateral fin-fold hypothesis 



This hypothesis was developed simul- 

 taneously by Balfour, Thacher, and 

 Mivart. It is now the most generally 

 accepted. 



It holds that the paired fins are the 

 persisting remains of a once continuous 

 longitudinal fin-fold (essentially like that of 

 the unpaired median fins) which stretched 

 along each side of the body. In this, sup- 

 porting radials or soniactidia became de- 

 veloped as in the median fins and subse- 

 quently gave rise to the limb-girdles. 



Original formulation of this hypothesis. 

 Balfour, F. M. 1876.1, 1878.1, 1881.1; 

 Mivart, St. G. J. 1878.1, 1879.1; Thacher, 

 J. K. 1876.1. 



The principal support for this hypothesis, 

 from the evidence of comparative anatomy 

 and embryology, is to be found in the papers 

 of Dohrn, A. 1882.2 (vi), (ix); Harrison, 

 R. G. 1895.2; Haswell, W.A. 1883.2; 

 Mayer, P. 1886.1; •Mollier, S. 1893.1, 

 1895.1; •Rabl, C. 1901.1, 1913.1; 



Wiedersheim, R. E. 1886.2, 1892.1. 



Lesser papers supporting this hypothesis. 

 •Baur, G. H. 1885.1, .2, 1887.1, .2, 1888.1; 

 Broom, R. 1913.3; Cope, E. D. 1890.1, 

 1892.6; Cunningham, J. T. 1884.1; 



Gregory, W. K. 1911.1, .2; Gregory, W. 

 K. & Adams, L. A. 1914.1; •Miiller, E. 

 1909.1; Ryder, J. A. 1885.14, 1887.3; 

 Thompson, D. W. 1886.1; Sauvage, H. 

 E. Add. 1903.1. 



Embryological evidence: the embryo of an 

 ancient type of shark, Heterodontus (Ces- 



