152 PROF. G. B. HOWES AND W. RIDEWOOD ON [Mar. 6, 



betrachtet, werden auch fiirderhia die ' uberzahligen ' Finger und 

 Zehen .... sondern als atavistische Bildungen angesehen werden 

 diirfen." 



Baur is, of all later writers, the one who has done most to combat 

 this doctrine. He advances (1, p. 68 et seq.) equally good argu- 

 ments for regarding these so-called supernumerary digits as purely 

 secondary and adaptive structures, laying, at the same time, great 

 stress upon their late appearance, especially in the case of the pre- 

 hallux itself. The advocates of the opposite belief^ seek shelter under 

 the stronghold of the Enaliosauria, but recent investigation at least 

 suggests that the paddles of those beasts were specialized derivatives 

 of pentadactyle predecessors ^. 



We trust to have already shown satisfactorily that the uaviculare 

 can no longer be regarded as the hallux-tarsal, as Born supposes ; and 

 that admitted, it follows that the pre-hallus conforms to the struc- 

 tural requirements of a sixth digit. More than this cannot be said 

 at present, and further speculation would be useless until the 

 connecting link between the cheiropterygium and its piscine pre- 

 decessor shall have been discovered. For this we look to the 

 palaeontologist. 



Setting aside further discussion as to the exact significance of the 

 pre-hallux itself, we cannot refrain from regarding that fragmentary 

 dismemberment of its outer free border, above represented, as an 

 additional argument for the views of Leydig and Baur. If the con- 

 verse one be justifiable, we should have ample ground for pleading 

 the cause of an octodactyle " Urform," and this would be prima facie 

 no advance at all. 



There is a growing tendency to attach too much importance to 

 gristly fragments such as those now under consideration, and it is 

 binding on those who may yet deal with these supposed vestiges 

 (especially as manifested in the higher Vertebrata), that they shall 

 determine at the outset, with greater accuracy than has hitherto been 

 done, what precise relationships they bear to the soft parts. If not, 

 the question bids fair to be reduced ere long to the condition of a 

 reductio ad absurdian. 



Fore Foot. 

 a. Metacarpals and Phalanges. — The poUex of the Anura under- 



' Parker writes (P. E. S. vol. 42 (1887), p. 67), "I Lave frequently noticed 

 that aborted parts, like overshadowed plants, are late to appear, and soon 

 wither, or are arrested in their growth." 



- Baur, •' Bemerkungen iiber Sauropterygia und Ichthvopterygia," Zool. 

 Anzeiger, 1886, pp. 245-252 ; also " Die Ab.stammung d. Auinioten Wirbeltb.," 

 Biolog. Centralbl. Bd. 7 (1887), pp. 481-493. See also "On the Phylogenetic 

 Arrangement of the Sauropsida," ' Journal of Morphology,' Boston, vol. i. 

 no. 1 (1887), pp. 93-104 ; the di.?covery by Gadow and Baur (herein recorded) 

 of supernumerary phalanges in the manus of Halicore and JIanatiis is most 

 welcome at this juncture. See also Baur, ■' Ueber den Ursprung d. Extrenii- 

 taten der lehthyopterygia," Bericht u. d. sx. Versammlung des Oberrheinischen 

 Geolog. Vereins, 1887. 



