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Show 704 MISS B. LINDSAY ON THE AVIAN STERNUM. [Julie 16, correspond exactly with those drawn from actual specimens in different stages (see Plate XLIV.). , f It is to be clearly understood that the broadening median end ot the clavicle, which Gotte describes in its condition during the 8th day of incubation, and interprets as an interclavicle, has nothlllg t0 do with the broad median end of the triangular clavicle figured below. The clavicle becomes uniformly thin throughout its length toward the close of the 6th day, as shown in diagram 3, fig. II. 1 2 3, show changes in the shoulder-girdle of the Chick, late on the 5th day of incubation ; 4, shows its condition during the 6th day ; and 5, its condition late on the 6th day, when the coracoid bone has acquired its sternal attachment and the coracoid and scapula have almost separated. The view above suggested with regard to the presence of a rudimentary precoracoid in the Chick at a early stage, is borne out by comparison of the condition of the internal part of the coracoid in various types. Beginning with the Ratitae, we see that where the precoracoid is apparently lost, there seems to be a rudiment of it remaining in the form of a process of the coracoid, situated in Dromaus (Plate XLIV. figs. 15 and 16) just beneath the clavicle. In Casuarius it seems possible that the area of bone extending internally to the foramen or incisura coracoidea* is also comparable with the precoracoid, since in Struthio the said foramen is situated near the internal margin of the bone ; but whether this precoracoid area is not rather a new growth of the coracoid than the homologue of the Struthionic precoracoid, is very uncertain. The peculiar marginal foramen seen in Plate XLIV. fig. 7 is seen partly developed, occasionally, in the Ostrich, where the precoracoid is present-a fact which supports the 1 This gives a passage to one of the nervi brachiales inferiores; this nerve supplies the in. supracoracoideus (called pectoralis minor elsewhere throughout this paper). |