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Show 584 MR. J. B. SUTTON ON THE DEVELOPMENT [June 2, but the basisphenoid and its associated nuclei are in no small degree interesting. Mr. Parker, in his very valuable paper, " On the Skull of the Common Fowl1' (Phil. Trans. 1869), introduces us to two very remarkable bones which he names the basitemporals. I will describe them in Mr. Parker's own words : - " The subcranial region, which in the Frog is ossified by the basitemporal wings of the parasphenoid, is here supplied with a pair of distinct and large basitemporal bones which extend from near the median line, beneath the cochlea and so far outwards as to constitute a floor for the tympanic cavity ; their anterior limit is near the fore margin of the alisphenoid cartilage. These ossifications arise in a thick weft of fibrous tissue in the hinder part of the palate ; the matrix is abundant in the middle line, extending forwards to the bone next to be described. The Eustachian tubes run forwards and inwards above the anterior edge of these bones, and meet in the middle line beneath the pituitary fossa"1. The Fowl's basitemporals are shown on Plate X X X V . fig. 1. It is needful to explain what is here meant by the basitemporal wings of the parasphenoid. Underlying the Frog's skull (as shown in Plate X X X V . fig. 2) is a dagger-shaped bone termed by Prof. Huxley the parasphenoid, but it is simply the representative of the vomer of the mammalian skull: the lateral portions marked L in the figure are what Mr. Parker refers to as the basitemporal portions. The morphological value which the latter writer places upon the bird's basitemporal is so singular that it is needful again to quote his own description, contained in a footnote in the "Fowl" paper:-"From a careful comparison of these parts in the lower Mammalia with those of man, I feel satisfied that the bony lingulae in that class answer to the basitemporal rudiments of the parasphenoid" (p. 770). This comparison was first suggested to Mr. Parker by Prof. Huxley, who states in a footnote in one of his admirable 'Lectures' that " Mr. Parker agrees with m y suggestion that the basitemporals of the Sauropsida are the homologues of the lingula sphenoidales of M a n " (p. 220). M y intention is now to proceed to show beyond all doubt that the "suggestion" and the " agreement" are out of harmony with the facts of the case and opposed to the usual methods of morphological reasoning. The lingulae of the Mammalian sphenoid have no relationship whatever with the basitemporals of birds. The proof is as follows :-The basitemporals, and no one doubts the facts, arise in membrane. It is a well-establisheJ truth that a bone preformed in cartilage cannot be homologous with one simply of membranous origin. The basitemporals are membrane-bones; the lingula? are preceded by cartilage. On this ground alone the evidence of identity fails. On Plate X X X V . fig. 3, is represented the base of the skull of a young Ostrich (Struthio camelus): two distinct osseous nuclei are seen lying on either side of the basisphenoid, between it and the alisphenoid ; they are developed in cartilage, thus in mode of ossification as in their relations they correspond to the 1 Morphology of the Skull, p. 231. |