62 PKOK G. B. HOWES AND ME. H. H. S WIJSIS 1 EETOJN' ON THE 



Born, as is well known, gave it as characteristic of the Lacertilia that tarsalia 1 

 and 2 were probably united with the corresponding metatarsals ; and in this lie has 

 been followed by Bayer (p. 24o), who claims a phylogenetic union for these ! Osawa 

 rightly figures the second tarsale of Sphenodon as distinct ; and we find that from 

 Stage Q (fig. 15) to the adult state this is present as an independent element (as in 

 fig. 18) which becomes extensively ossified. 



Perrin asserts (95. pp. 44 & 97) that five separate distal tarsalia are present, 

 and his figure 9 may illustrate but does not adorn his text! We are at a loss to 

 understand what he has figured ; but one thing certain is that in ascribing three 

 phalanges to the fifth digit he is in agreement with Bayer, who is inclined to regard 

 the hooked bone, which by its angulated head articulates with the outer face of the 

 fourth tarsale, as the fifth of that series. As a salient objection to regarding this as a 

 metatarsal he seeks to show that on the Giintherian determination Sphenodon would 

 be an exception to the rule among Lizards in possessing more than three phalanges 

 to the fifth digit ; but it does not occur to him that this statement is tantamount to 

 admitting that the angulated bone is in most Lizards a metatarsal, and that it thereby 

 nullifies his argument. Dismissing for the moment the facts of development, the 

 discovery by us that a specimen preserved in the R. College of Surgeons Museum is 

 possessed of three phalanges on the outermost digit of one hind limb, and four on the 

 other, dispenses with the necessity for further discussion of this point, except to remark 

 that among the Chelonia, Pleurodira (Emydura) for example, we meet with a quadri- 

 phalangeate fifth toe. The matter is clearly one lying within the range of individual 

 variation. 



Developmentally, this bone, angulated from the first period of its differentiation 

 (Stage Q, PI. VI. fig. 16, v.), ossifies at R (PL VI. fig. 17), at the same time and in 

 the same manner as the other metatarsals ; and we have already pointed out that the 

 tarsal elements do not ossify until T, when the metatarsals are formed. And were 

 further proof needed of its metatarsal homology, it is forthcoming in the totally 

 different manner of ossification of the carpus and tarsus and the metacarpals, meta- 

 tarsals, and phalanges the former ossifying endosteally, the latter ectosteally. 



There is no trace in Sphenodon of tarsale 5 actual or potential, and no evidence 

 developmentally for the belief of Baur that it is incorporated in the fourth tarsale 

 (Zool. Anz. Bd. ix. p. 189) 1 . It seems to have vanished even from the ontogenetic 

 record. 



Concerning the proximal tarsal series, Osawa describes one confluent element; and 

 Giinther evidently had to deal with a specimen in which they were just uniting, for 

 the " suture " to which he refers as " scarcely visible " is recognizable, as in our PI. VI. 



1 We are disposed to believe, with Forsyth Major (Trans. Linn. Soc., ZooJ. vol. vii. 1890, p. 510), that the 

 compound nature of the " cuboid " is seriously open to doubt. 



