1885.] MISS B. LINDSAY ON THE AVIAN STERNTTM. 703 



It is always stated that the coracoid and scapula of the Chick 

 arise as a single plate, but the various specimens examined did not 

 bear out this description. The shoulder-girdle of the 5 days' chick, 

 in which the pericardial cavity is not quite closed, is shown in figs. 

 4 and 5, Plate XLIV. It consists of three pieces, whereof the middle 

 one is partly attached to that nearest the median line. According 

 to Gotte, who maintains the usual view that the scapula and coracoid 

 form a single plate, and who further describes the episternal pro- 

 jection of a 5 days' Chick as clearly distinguishable from the clavicle 

 itself, these three pieces would be interpreted as coraco-scapular 

 plate, clavicle, and interclavicle ; but this interpretation, rendered 

 doubtful by the early separation of scapula and coracoid, already 

 noticed in the Ostrich and the Gull, is rendered impossible by com- 

 parison of subsequent stages, Plate XLIV, figs. 3, 4, .5, and 6, 

 show how the median piece gradually elongates, without growing 

 thicker, and forms the clavicle, while the intermediate and the dorsal 

 piece fuse to form the coraco-scapular mass usually described, which 

 was found to exist early on the 6th day (fig, 6). The late date 

 of its appearance suggests that this fusion may represent rather a 

 Struthionie than a pre-Avian condition. 



The interpretation as clavicle of the median piece which is partially 

 attached to the intermediate one, agrees with the description of 

 Rathke, who says that at an early stage the coracoid and clavicle are 

 united dorsally but not ventrally ; nor is it inconsistent with that of 

 Gotte himself, who says the end of the coracoid passes under the 

 clavicle, which is the same thing in other words. Now the median 

 piece, though posteriorly free, is united anteriorly to the coracoid ; 

 and this anterior union is dorsal, for the two pieces appear separated 

 by a crack when seen from the surface (cf. figs. 3 and 4), yet on 

 dissection they are found united below. 



At first sight the relative positions of the two pieces present a 

 difficulty in the interpretation just given, viz., that they are placed 

 end to end, not parallel as in the adult, so that the clavicle is 

 separated from the scapula by the whole length of the coracoid. 

 The same difficulty, however, attends Gotte's account of the relation 

 of the two parts; since, although he traced the end of the coracoid 

 under the outer end of the clavicle, he expressly states that he failed 

 to trace it far towards the median part of the clavicle ; in other words, 

 he also found the two placed, at this stage, end to end. 



Again, a second difficulty lies in the fact that the intermediate 

 piece of the shoulder-girdle is triangular, which the coracoid is not. 

 During the 5th day, however, it loses this triangular shape, and is no 

 longer found to be, as at first, a flat mass, comparatively thin. This 

 change suggests that possibly the anterior apex of the triangle is 

 equivalent to the precoracoid of the 5 days' Gull (which also forms 

 a mass lying between the clavicle and scapula), and that the clavicle 

 is gradually carried up towards the dorsal end, by the atrophy of 

 that part, with which it is in close connection. This theory is best 

 explained by the following series of diagrams. Reference to the 

 Plates will show that, although themselves diagmmraatic, these figures 



