704 



MISS B. LTNDSAY ON THE AVIAN STERNUM. [JuUC 16, 



correspond exactly with those drawn from actual specimens in dif- 

 ferent stages (see Plate XLIV.). 



It is to be clearly understood that tlie hroadening median end of 

 the clavicle, wliicli Gotte describes in its condition during the 8th 

 day of incubation, and interprets as an interclavicle, has nothing to 

 do with the broad median end of tiie 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. 



Fig. II, 



2, 3, sbow changes in the shoulder-girdle of the Chick, late on the 5th day of 

 incubation ; 4, shows its condition during the Gth day ; and 5, its con- 

 dition late on tlie fith day, when the coraeoid bone has acquired its 

 sternal attachment and the coraeoid and scapula liave almost separated. 



The view above suggested with regard to the presence of a rudi- 

 mentary precoracoid in the Chick at a early stage, is borne out by 

 comparison of the condition of the internal jiart of the coraeoid in 

 various types. 



Beginning with the Ratiise, 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 coraeoid, situated in DromcBus (Plate 

 XLIV. figs. 1.5 and IG) just beneath the clavicle. In Casuarius it 

 seems possible that the area of bone extending internally to the 

 foramen or incisura coracoidea^ is also comjiarable with the precora- 

 coid, 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 coraeoid than the homologue of the Struthionic 

 precoracoid, is very uncertain. The peculiar marginal foram.en seen 

 in Plate XLIV. fig. 7 is seen partly develojied, occasionally, in the 

 Ostrich, where the precoracoid is present — a fact which supports the 



^ This gives a passage to one of the nervi brachiales inferiores; this nerve 

 supplies the m. supracoracoideus (called pectoralis minor elsewhere tliroughout 

 this paper). 



