MOEPHOLOGT OF THE GALLINACE^E. 223 



brane or a membrane bone, the simple clavicle (cl.) — the early condition of one fork of 

 the Y-shaped f urcula. The almost hyaline cartilage developed at the top of the clavicle 

 at a later stage (op. cit. plate 16. fig. 9, m.sc.s.), or after 10 days' incubation, does not 

 belong to the anteroinferior bone or precoracoid, but to the acromial region of the 

 upper bar, or scapula. I call it the " meso-scapular segment." 



IX. — Further Development of the Sternum and Shoulder-girdle m the Chick and 



Adult Fowl. 



Miss Lindsay (op. clt. p. 701) says truly that in the Fowl a newer process arises on 

 the outer side of the main lateral metasternal bar, and in the Gull on the inner side. 

 Not only in the Gull is this the case, but in all birds, except the Fowls, that have two 

 pairs of metasternals. Thus the Gallinaceous birds are sharply divided off from their 

 neighbours by this antero-external, or rising, fork of the postcostal part of the sternum ; 

 the " Peristeropodes " as well as the " Alectoropodes " show this. The Pteroclidse and 

 Colunibidae do not possess this part, but form a submedian process as in the Gull ; whilst 

 the Hemipods and Tinamous have only one lateral process, like the Ostrich on one hand, 

 and the Goose on the other. But orderly as these processes seem, to be giving character 

 to this family and to that in their variation, they arise merely as a creeping backward of 

 the cartilaginous tissue, to be replaced to a great extent afterwards by bone, for the sake 

 of muscular origin and insertion. Single in the Rhea, Emu, and Cassoway, the meta- 

 sternum may develop four processes on each side, besides the double median plate. For in 

 the Turkey (Meleagris gallopavo, Plate XXV. fig. 1) the antero-superior outgrowth is 

 double, for a partial forking takes place, in the form of a fenestra ; whilst in the Caper- 

 caillie ( Tetrao urogallus) the median part is separated by a notch from a submedian lobe 

 (Plate XXV. fig. la). 



Prof. Huxley, in his paper on the Alectorornorphse (P. Z. S. 1868, p. 303), says : — " It 

 seems to me to be demonstrable that the long xiphial process of the sternum of Hemipodius 

 answers to the outer of the two metosteal processes of the Alectoromorphce, and not to 

 the inner, as Mr. Parker supposes in his paper on the Gallinaceous birds ; or to the inner 

 and outer together, as he suggests in his great work ' On the Shoulder-girdle and Ster- 

 num' (p. 187). Thus the sternum of Hemipodius is strongly Thiamine." It is seen at 

 a glance that this view of Professor Huxley is set aside by the notched median rueta- 

 sternum of Tetrao urogallus, and by Miss Lindsay's researches. Even my second view 

 of these, perhaps, is not really incorrect ; and the long single lateral metasternal of 

 Hemipodius and Tinamus is the true morphological representative of the forked 

 lateral metasternal of the Fowl. The long process is the same thing in Fowl, Hemipod, 

 Tinamou, Pigeon, and Sand-Grouse ; these last two have a new inner, and the Fowl a 

 new outer process. 



There is a fact of importance in this matter, namely, that in the Hemipod, Fowl, and 

 Ostrich- tribe, the ossification is by neat and clear ectosteal tracts, and not, as in most birds, 

 by a very generalized endosteal deposit, which only imperfectly separates, even for a 



34* 



