DEVELOPMEJST OF THE SKELETON OF THE TUATARA. 71 



ontogeny ; the investigation of Kiikenthal, which has brought to light the remarkable 

 fact 1 that the fourth and fifth digits of the Crocodilian fore limb are developmentally 

 hyperphalangeate — all testify to the great potentiality of the digital blastema ^, and do 

 away with the value of the mere numerical difference as a criterion of affinity. 



The question thus resolves itself into this — are the Terrestrial Vertebrata the 

 descendants of the afore-defined Batrachian-Reptilia or of Reptilian-Batrachia % The 

 problem for the immediate future lies in the study of the occiput, the sternal skeleton, 

 and the quadrate ; and, to our thinking, Sclerocephalus, with its multisegmented 

 and structurally simple " plastron," its " fanged " vomer, its elongated dentigerous 

 pterygoid ^, and its quadrate, points the way. 



It is certain, but most unfortunate, that in its earliest forms, the sternum, known to 

 us only in its definitive conditions, was cartilaginous, and has been lost to us in the 

 palseontological record. The discovery by Osborn, however, of a cartilaginous sternum 

 in the fossil state *, gives us hope. The decision must lie with the future. 

 Anatomist and palaeontologist must approach the question in the spirit of a combined 

 morphological brotherhood ; and its solution will mark an epoch in the progress of 

 the vertebrate morphology of the era of its discovery. 



Addendum, Nov. 16, 1900. 



Shortly after the proofs of this Memoir were revised for press, there reached us a recently- 

 published paper on the organogeny of Sphenodon, by Professor H. Schauinsland, of Bremen 

 {Archv. Mikr. Anal. Bd. Ivi. pp. 447-867). Although it came to hand too late for comment in 

 our pages, we observe from its perusal that it is in places erroneous, and that we should have lost 

 nothing by its earlier appearance, since its author is insufficiently acquainted with the literature 

 of the subject, and apparently ignorant of the recent important papers by Dendy, now more than 

 a year old. 



List of the more important Memoirs dealing with Sphenodon. 



83 



Albbecht, p. Note sur la presence d'un Rudiment de Proatlas sur un exemplaire de 

 Hatteria punctata. Bull. Mus. Belg. torn. ii. pp. 185-193. (First record of pro-atlas.) 



SSb. . Epiphyses osseuses sur les Apophyses epineuses des Vertebres d'un Reptde 



(Hatteria punctata. Gray). Bruxelles, 1883. Pp. 1-6. 



86". Baur, G. Die zwei Centralia im Carpus von Sphenodon (Hatteria) und die VVirbel von 

 Sphenodon und Gecko verticillatus, Laur. (G. verus, Gray) . Zool. Anz. Bd. ix. pp. 188-190. 



' Kiikentlial, W. : Morphol. Jahrb. Bd. xix. 1893, p. 50. 



" In a manner akin to that of the passing "jointing'" of the hyoid cornu described in the text {a7itea,p. 48). 

 ' It is unfortunate that its parasphenoid is unknown, but it must assuredly have possessed one, and that 

 probably dentigerous. 



* Osborn, H. F.; op. cit. antea, p. 14. 



