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Show 400 PROF. HUXLEY ON THE REPRESENTATIVES OF [May 27, Such developmental evidence as exists is entirely in accordance with the view of which these anatomical facts appear to me to afford a sufficient demonstration. Rathke distinctly states that in Coluber natrix the stapes results from a modification of the upper end of the hyoidean arch. Prof. Peters does not allude to this important circumstance ; and, what is still more remarkable, in giving an account of his observations on the condition of the parts in a young Crocodilian embryo, he does not point out that Rathke's statements on the same topic are diametrically opposed to his own. The embryo examined by Prof. Peters (/. c. p. 595, figs. 1, 1 a) was 70 millimetres, or nearly 3 inches long. He says that the quadrate bone was "angelegt," but contained " neither cartilage nor bone;" so that it is not obvious what the histological condition of the part referred to may have been. But in an embryo of Aligator lucius of less size (2" 2"' long, the skull measuring 7'") Rathke ('Untersuchungen fiber die Entwickelung und den Korperbau der Krokodile,' 1863, p. 34) found the quadratum quite cartilaginous. "The quadrate bone resembled in form that of young and adult specimens of Alligator lucius, but was narrower and thinner, in proportion to its length, in its lower part, which is provided with a shallow articular excavation. It consisted of cartilage ensheathed in its middle third by a bone. By its broader and flatter upper half it was loosely attached to the outer surface of the cartilaginous auditory capsule, in front of and above the fenestra ovalis "With the quadrate bones articulated two long and, on the whole, slender Meckelian cartilages, which extended to the mandibular symphysis. For the greater part of their length they were cylindrical, and diminished in diameter very gradually from behind forwards; posteriorly, however, where they were connected with the quadrate bones, they were a good deal enlarged. An absolutely and relatively short, hook-like prolongation extended beyond the articulation. The thinner and longer cylindrical portion of each was loosely invested by five very thin, but completely ossified, plates, which enclosed it, as in a sheath, though they were separated by larger or smaller intervals. At a later period these plates grow and become closely united, thus giving rise, as in other Reptiles and in Birds, to the greater part of each ramus of the mandible. But of Meckel's cartilage only the enlarged part ossifies, and thus gives rise to the articular piece of the lower jaw." How is this discrepancy to be accounted for? Unfortunately I have been able to procure no specimen of an embryonic Crocodile so small as either of those here described; but Prof. Peters's figures (Taf. i. figs. 1, la) leave very little doubt on my mind that the cartilage which he marks m, and imagines to be his "malleus" (the suprastapedial cartilage) is really the quadratum, the articulation of which with Meckel's cartilage takes place in the ordinary way, and that i, called the columella (or stapes), is neither more nor less than the pterygo-palatine cartilage. The most cursory glauce |