508 PROF. HOWES AND MR. A. M. DAVIES ON THE [DeC 4, 



rise, by transverse segmentation and subsequent ossification, to extra 

 terminal distal segments as found in existing Cetacea.'' His chief 

 ground for this belief is the assertion that (p. 1014) in Glohio- 

 cephalus, " while the metacarpal elements and first three or four 

 phalangeal segments of the second and third digits ossify simul- 

 taneously, the four to six extra distal segments ossify in succession 

 towards the distal periphery, the terminal elements of the digits 

 being the last in which ossific centres appear." It must suffice to 

 state here that all recent advance is opposed to this extravagant 

 hypothesis, and that it finds no support in fact (rf. Leboucq and 

 Kiikenthal). Baur, in criticising Leboucc|'s deduction (12. p. 208) 

 that " la main des cetaccs a conserve des caracteres tout a fait 

 primitifs, et ne pent otre derivee par adaptation de celle d'aucun 

 mammifere actuel," naively remarks (1. p. 493): " wenn also die 

 Embryonen verschiedener Cetaceen mehr Phalangen besitzen als 

 das erwachsene Tier, so beweist dies nur, dass die niichsten Ahnen 

 der Cetaceen, welche aher schon luakre Cetaceen waren, mehr 

 Phalangen besessen haben." Here is, in other words, the refrain of 

 our own contention, and we regard Leboucc|'s retort (13. p. 534 "> 

 that it " versetzte einfach die Frage, ohne dieselbe zu losen " as based 

 on a misinterpretation of its meaning'. 



Supernumerary phalanges have been supposed to represent the 

 products of subdivision, on elongation, of shorter predecessors, and 

 this conceived mode of origin would find a close parallel in the paired 

 ossification, under lateral expansion, of the supra-occipital and inter- 

 parietal in the Cetacea themselves if not in the occasional replace- 

 ment of greatly expanded bones in Wormian elements. Dixey, 

 describing the ossification of the terminal phalanges in the Mammalia, 

 furnishes some reason for believing that (3. p. G5) "the distal 

 extremity of the ungual phalanx corresponds morphologically with 

 the centre of the diaphysis in other long bones;" and this deduction 

 might conceivably lend support to the above-named supposition. 

 "We are not of this opuiion. We hold such differences as exist 

 between the terminal and penultimate phalanges to be purely 

 adaptive. 



Our researches record, for the first time, the initial stages in the 

 actual primary development of a supernumerary phalanx, and it is 

 deserving of note that the most complete difi'erentiation undergone 

 by such is realized in the animals with which we deal. That it 

 arises as an intercalary structure and is a direct derivative of the 

 syndesmosis, is irrefutable. In seeking to apply these facts to the 

 Cetacea, we quite agree that the " Hxjperphalangie'''' is "an adaptive 

 phalanx-hke segmentation " (Kiikenthal, 10. p. 641) ; but we 

 \^ould be inclined to substitute for the words "of an elongated 

 cartilaginous ray borne upon the third phalanx" — of a blastema 

 productive of both phalanges and inter-phalanges, and that argument 

 from analogy to the only known facts of development would lead us 



^ A knowledge of the early condition of the digits in Platanisfa is much to 

 be desired, for specimens iji luy teaching collection and one in the Museum of 

 Natural History show conspicuous traces of a fourth bony phalanx. — G. B. H. 



