12 PROF. G. B. HOWES AND MR. H. H. SWINNERTON ON THE 
attention, mainly as the result of paleontological discovery by Cope!, Gaudry 2, and 
Fritsch*; leading to the recognition of the so-called rhachitomous, embolomerous, and 
other similar conditions, which have received at the hands of subsequent investigators 
correspondingly appropriate names. Both on the embryological and the paleonto- 
logical sides, a considerable amount of evidence has been brought forward for the 
belief that some such complex type of vertebra as these, 7. e. one in which each vertebral 
segment was made up of a series of paired elements, was the ancestral one, and that 
the various types of vertebral structures characteristic of the living groups may have 
resulted from diverse modification (inequality of growth and suppression) of these. 
And, in the attempt to substantiate this belief, Manner, in the latest paper* on the 
subject, has sought to show that from the first period of its differentiation in cellular 
tissue, the individual * sclerotome ” of the Lacertilian is a compound structure. Goette, 
basing his arguments, like Manner, mainly upon the study of the Reptilian backbone, 
has concluded ® that the vertebre of the living “ digitata” have arisen from the embo- 
lomerous type, and he regards the rhachitomous type as ‘neither primitive nor 
independent, but transitional.’ If, however, the relationships of these are really direct, 
we would rather transpose the order, since we regard the greater extension of the 
skeletogenous tissues, and consequent deeper constriction of the notochord, occurring in 
the embolomerous type as indicative of advance upon the rhachitomous, as already 
pointed out by Gadow®. He, working on this basis, has simplified our conceptions of 
the fundamental constitution of the diverse forms of vertebral structure represented 
among the living vertebrata, beyond his predecessors, by the introduction of a 
systematic terminology based on the supposition that all surviving forms of vertebra 
are constituted more or less of two pairs of dorsal and two of ventral elements 
symmetrically disposed, and that’? “the solution of the composition of the vertebral 
column is given by the metameric repetition ” of these, ‘‘ the origin of which can be 
’ , 
"and “inter-” ‘ dorsalia,” “ basi-” and “ inter- ’ 
“‘ventralia,” are most welcome ; and the arguments and conclusions drawn by him 
traced in fishes.” His terms “ basi- 
certainly furnish a possible explanation of some of the great anomalies arising out of 
the mere study of the adult vertebral column among living forms—as, for example, the 
intervertebral disposition and independence of the “chevron bones” of the Amniota, 
and the vertebral disposition and confluence with the vertebral bodies of the “ hemal 
arches” of the Urodela. 
1 Cope, E. D.: Americ. Nat. 1878, p. 8327; Proc. Americ. Philos. Soc. vol. xvii. 1878, pp. 510-526 ; Trans. 
Americ. Philos. Soc. vol. xvi. 1886, p. 243. 
* Gaudry, A.: Enchainements d. Monde anim. Foss. Prim., tom. i. (Paris, 1883), p. 263. 
* Fritsch, A.: Fauna d. Gaskohle d. Permform. Bohmens, Bd. ii. 1889, pp. 14 & 24. Cf. also Baur, G.: 
Biol. Centralbl. Bd. vi. 1886, pp. 332 & 353. 
* Manner, H.: Zeitschr. wiss. Zool. Bd. Ixvi. 1899, p. 43. 
> Guette, A.: Zeitschr. wiss. Zool. Bd. lxii. 1897, p. 390. 
* Gadow, H.: Phil. Trans. vol. 187 B. 1896, p. 1. 
7 Op. cit. p. 50. 
