MOEPHOLOGT OF THE GALLINACE^. 231 



as tlie three distal tarsals are, further down. In the Ostrich, in Opisthocomus, and in 

 some others, the ascending process is a long- striji of cartilage ending in a point above ; 

 in the Chick it is shorter, and it is shorter still in the Alcidse and Pelecanida3. 



As for the intermedium being a mere " outgrowth from the tibiale," the view taken 

 by Miss A. Johnson and Dr. G. Baur (Johnson, op. cil. p. 25), and by my sou, Prof. T. 

 J. Parker, my answer is, that it is almost equally related to both tibiale and fibulare, 

 and that it is above both of them, and that no outgrowth or ascending periosteal process 

 to the tibiale is possible at any time, as that part ossifies late and internally, and the 

 whole mass is joined to the end of the tibia, and ankylosed to it as soon as the tibiale 

 and fibulare are perfect. In the Swan the ectosteal sheath of the long and thoroughly 

 chondrified intermedium begins at the middle of the incubating period ; it is far 

 advanced in embryos four-fifths ripe. In Cygnets one month old, the tibiale and 

 fibulare are small endosteal nuclei, deeply hidden in the common proximal tarsal 

 cartilage. 



After half a century's research in matters of this kind, I never found a secondary part, 

 any periosteal flange, or process to be developed before the part of which it is the mere 

 " outgrowth." 



The high position of this epipodial segment, its great relative length in many birds, its 

 early chondrification, its narrow basal isthmus, its early ossification, and that in a 

 manner not like a tarsal, but the same as in the tibia and fibula, /. e. by ectostosis and 

 not by endostosis, and its evident homology with the intermedium of the Ichthyosaurs 

 are quite satisfactory to me as to its nature. Dr. Baur (" Ueber den Ursprung der 

 Extremitaten der Ichthyopterygia," Separatabdruck aus dem Bericht iiber die XX. 

 Versamml. des Oberrh. geol. Vereins) has given outline figures of the upper part of the 

 fore limb of the " Mixosauridae," " Ichthyosauridte," and " Ophthalmosauridse." In the 

 first and second of these there is a " pisiforme," making four in the proximal row of 

 carpals. In the third type there are only three ; and Dr. Baur, for some mysterious 

 reason, known to himself only, letters these three as r, u, p. I should letter them 

 R, I, TJ. It is pure conjecture that the pisiforme should get between the humerus and 

 idnare, and thus be a third " epipodial " segment. To me the pisiforme looks like a 

 stray remnant of some lost ray of the ichthyopterygium. Thu.s the middle of these 

 three nuclei appears to me to answer to the intermedium, which Marsh finds in 

 Sauranodon (Amer. Journ. Sc. vol. xix. Feb. 1880, pp. 169-171, fig. 1). The figure 

 given there is of the hind limb, but that does not afi'cct the question. Professor D'Arcy 

 "W. Thompson (Jom-n. Anat. & Phys. vol. xx. pp. 1-4) gives, in his fig. 1, diagrams 

 showing that in the Ichthyosatirus the intermedium may lie close to the " propodium " 

 (femur), between the tibia and fibula. I had satisfied myself that the intermedium of 

 the Chick's hind limb was not a tarsal segment, bu.t a shaft-bone of the leg (" ej)ipo- 

 tlium"), before I saw how this view harmonized with what Marsh has told us of 

 Sauranodon, and D'Arcy Thompson of Ichthyosaurus platyodon. 



Of the three distal tarsals that cap the three developed metatarsals, only that over 

 the third is chondrified in the 1st stage. The tarsal substance is soft, right and left ; 

 it is also postero-internally, where the "scaphoid" (centrale) is formed. The tight 



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