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Show 16 PROF. G. H. HOWES ON THE SKELETON AND [Jail. 18> denies the existence of these, as has previously been stated ; but them be present or not, it is certain, should Giinther's observation hold good, that they cannot indicate the original lines of separation between pro-, meso-, and metapterygia, as now understood. IV. On the proximal Postaxial Elements of the Ceratodus Pelvic Fin. The cartilage which I have already described (figs. 1 and 3) as directly connected with the postaxial border of the basal mesomere of the Ceratodus pelvic fin is ray-like, but relatively powerful, in one of the two specimens (fig. 1). In the other (fig. 3) it is altogether smaller and segmented into but two pieces, instead of into three, as in the former specimen. While it here meets the distal end of the proximal mesomere, it is much more intimately connected with the second piece of the axis than in the former specimen ; but on the supposition that the cartilage is homologous in both fins, its condition in fig. 3 is precisely that which would result from a further reduction of that of fig. 1, such as there is good ground to believe, for reasons previously alleged, has actually gone on. In the second specimen the cartilage in question is further interesting, in that it bears one and is in close connexion with a second of the proximal parameres. In the specimen figured by Giinther (14, pl. 36. fig. 4) already referred to (p. 5), the proximal piece of the axis bears two cartilages. Fig. 4 is a reproduction of his drawing. The distal cartilage is ray-like, and stands related to the base of the proximal mesomere as does an ordinary postaxial paramere to the corresponding border of a typical mesomere. The proximal cartilage appears to have been free of the basal piece altogether. It is, as shown in the figure, plate-like, and I have little doubt but that it was formed by the confluence of the basal ends of at least the two rays which it carries. These skeletal elements, as they stand in Giinther's specimen, combine the characters of those of the two described by me (figs. I & 3). The postaxial parameres are, as in m y specimens, much simpler than usual, and the whole series of lateral rays are in his fin more uniformly distributed than in general. The basal plate is (fig. 4, mt.), like the corresponding bar of fig. 1, in near relationship with the proximal mesomere, although but loosely connected therewith ; while it agrees with the corresponding element of fig. 3 in giving attachment to a couple of rays. Comparing the proximal postaxial elements of my two specimens and Giinther's figure with the corresponding region of the pectoral fin-skeleton, and reflecting that the typical metapterygium is formed by a confluence of the basal ends of the rays of that region, I incline to the belief that the vestiges in question represent that lobe of the fore limb which I claim as the metapterygium, together with its associated rays. Should the cartilages now under discussion have the morphological value which I am seeking to establish for them as probable, the well-known views of Gegenbaur (10, 11), and Huxley (19) will |
