222 PROF. W. K. PAEKER ON THE 



work on the " Shoulclei'-girclle and Sternum," I have shown this sternal plate in its two 

 primary moieties in the Lapwing (plate 15. fig. 1). In this 1st stage (Plate XXII. and 

 Plate XXV. fig. 2) the two moieties are becoming fused together, and each is contributing 

 to the formation of the keel. The essential or costal part of the sternal moieties is here 

 seen to be a small crescentic tract of cartilage passing, below, into a much larger tract, 

 which has its teleological meaning very clear : it is for articulation of the sternum with 

 the coracoid and for the " origin " of the huge pectoral muscles. In front, above, a pro- 

 cess, the rostrum, grows forwards, the use of Avhich is for the attachment of the liga- 

 ments of this part of the trunk ; this is separated by a round notch from the projecting 

 sternal keel, which already grows backwards, far behind the proper costal region of the 

 sternum ; it has a right and left dilatation below the great notches and ends in a point, 

 behind. 



I have already mentioned that the first sternal rib is often transitory ; the projection in 

 front of that, the precostal process, properly belongs to those cervical vertebrge which 

 have segmented riblets. There is a traceable abortion of these parts in the Chick, espe- 

 cially in still earlier stages (see Lindsay, op. cit. p. 708, fig. 5). 



The costal tract ends, behind, in soft tissue, which is beginning to bifurcate ; it will form 

 the antero-external xiphoid (metasternal) process and the external proper. I shall 

 refer to this point again. 



In describing the shoulder-girdle at this stage, I must refer again to Miss B. Lindsay's 

 paper {op. cit.), which contains many valuable remarks and observations, but in which 

 she has misread and misconstrued my former work (" Shoulder-girdle and Sternum ") to 

 a degree that is humiliating to me, for this suggests that I must be a confused writer. 



I must, however, in self-defence, remark that the three main parts of the shoulder-girdle 

 figured by Miss Lindsay (p. 704, fig. 11) arc not, in my eyes, true differentiated skeletal 

 elements, but thickened masses of tissue that contain the embryonic cartilage, which will 

 be differentiated into cither hyaline cartilage, or be at once developed into bony tracts 

 (parostoses). The latter are exoskeletal structures ; the former endoskeletal. 



As I have said before, hyaline cartilage is my "cue;" before that is formed, anything 

 may be made of anything ; and thus Morphology is at the mercy of each individual 

 worker *. 



The endoskeletal part of the shoulder-plate is a curved bar, partly segmented at its 

 lower third, and then bent backwards considerably ; the iipper sword-shaped tract is the 

 scapula {sc.) ; the lower, phalangiform bar is the coracoid {cr.). There is an antero- 

 inferior tract, but this is not composed of cartilage. In Progs and Tortoises and in the 

 African Ostrich, there is such an antero-inferior cartilaginous bar {op. cit. plates 5-7, and 

 12 and 17). But the Powl is like the Crocodile in this respect {op. cit. plate 11. figs. 7 

 and 8). There is at this stage a slight rudiment of a special nucleus in front of the head 

 of the coracoid, but it develops no further, and all the tissue then becomes either mem- 



* I must here refer to what may be called a diseased condition of Biological research. However young and inex- 

 perienced the workers, no evidence not obtained by them, individually, is to be taken on trust for a moment ; if Science 

 is to run in such narrow ruts, its progress will be slow. 



