10(5 



THE EXTINCT BATRACHIA, REPTILIA 



A reasonable inference is that they were continuous, and I have taken this view. (Proc. Acad., I860, p. !5l(i.) There is 

 however an objection to (his position. One is that the astragalus does not extend across the entire end of the tibia, 

 and presents a, smooth surface, perhaps an articular, at its outer extremity. This must have been in contact with a 

 small astragalus or with a malleolar extremity of the fibula. The thin external expansion of the tibia could support 

 but little weight, and as the condyloid convexities of the astragaloid piece arc nearly equal, there would seem to bo 

 little need of additional condyloid face. Should however the fibula have descended to tins point, its course must 

 necessarily have been alongside the ascending process of the astragalus, but not in contact with it. There is no trace 

 of such contact, as the process presents externally an obliquely rounded surface, ending in an angular margin with 

 a posterior flattened face. 



Two other examples only of this structure arc known in the vertebrata, one of which I find mentioned in Ouvier 

 Osscincns Fossiles, X, p. 204, Tab. 249, lis- 34-5. This author studied the distal extremity of a, tibia, with applied 

 condyloid astragalus, from llonlleur, which he was not able to assign to any known species or genus, but, which he, 

 with usual sagacity, includes in the chapter devoted to Megalosaurus. lie however regarded the face of the tibia 

 receiving the condyloid bearing bone, as the inner, instead of the anterior, stating that, the tibia, is laterally instead 

 of anteroposterior^ compressed, so anomalous is this structure among vertebrates, lie regarded the bone as the 

 astragalus, and did not perceive any connect ion between its anterior ascending apophysis and a fibula, partly because 

 a Qbula with distinct distal articulation was received with the same bones. 



Gegenbaur's demonstration of the nature of the ankle, joint among birds and reptiles at once, makes the nature 

 of the present case clear.* 



This tibio-tarsal bone possesses an articular facet on its exterior extremity, probably for conjunction with a 

 caleaneum which supported a, small second row tarsal and perhaps rudimental metatarsal and phalange. Its plane is 

 transverse and does not cover the whole extremity, the anterior margin and a knob on the anteroposterior part of 



the extremity projecting bey lit. Exterior to the middle of the upper margin of this piece and at the internal 



base of the ascending apophysis, it is perforate, as is the cavity above the condyles of the humerus in the higher apes, 

 and may have, received a similar coronoid process of a sea.phoides. 



As compared with the species examined by Cuvicr, this astragalus has a less elevated form; in Cuvicr' s specimen 

 the ascending apophysis was flatter, broader, and directed toward the calcaneal facet instead of from it; it lacked 

 the submedian perforation. Its tibial face appears to have been rounded, not angulate. The tibia presented an 

 ascending ridge, to the face of which the ascending apophysis was applied; in the Laelaps aquilunguis I, here; is 

 no ridge, the apophyses reposing in a slight concavity. This apophysis, like the slender portion of the fibula, is 

 composed of dense bone. 



Cuvicr describes at the same time a bone, of which he says "il ue serait pas impossible que 1'os (fig. ">'■)> fut la 



tele superieur du pcrone du pied que je viens de dec.nre." This piece has a shaft compressed at, right angles to the 



direction of its head, a form so unlike the fibube of known Dinosauria, including Megalosaurus and Laelaps, as to 



render such a relation to the before-mentioned tibia,, very doubtful. It is probablya metatarsus. 



The second example of the clasping astragalus with anteriorly directed condyle is the Poociloplcurum of Des- 

 longchamps. lien; the angle between tibia, and metatarsus has been even greater than in Laelaps. The ascending 



anterior ala is broader than in Laelaps, and appears to be complete and not continuous above with the fibula. 

 That it is in contact with the fibula, be states thus: "its infernal face is applied to the tibia, while its external was 

 without doubt covered in part by the inferior extremity of the fibula." This, with identity of form, between the 

 extremities of the fibula, and of the aseending process of the astragalus, in Laelaps, renders if probable that 1,1m rela- 

 tion is similar in the latter. I may add that, I suspect that Deslongchamps like others has reversed the relations of 

 the extremities of the fibula. If both the extremities figured by this author belong to if, if is much less attenuated 



than in Laelaps. 



The tibiae figure by Ouvier and Deslongchamps appear to belong to different, species, 'they differ in many 

 respects as figured. The former has a more contracted shaft than the other ; its extremity is less oblique ; the infe- 

 rior plate of the astragalus thicker and less produced ; the anterior plate in every way smaller. The species should 

 bo called Poecilopleurum gallicum. {Laelaps gallieui m. Pro. Ac. N. Sci., Phil., 1887, 235.) 



• See <;<'!< ii !j.i:ir, CarjnM and Tarsus; tarsus of Chick ninth day, Tab. 



