224 MR. W. P. PYCRAFT ON THE MORPHOLOGY AND 
external lateral process at its base. The pre-coracoidis wanting. The scapula is free, 
as in the young of the flightless members of this group. 
The furcula is slender and U-shaped. 
Tur DEVELOPMENT OF THE STERNUM AND PECTORAL ARCH. 
a. Sternum. 
Miss Lindsay’s [48] researches have shown that during development the sternum 
undergoes a process of shortening both anteriorly and posteriorly, at least in so far as 
its costal elements are concerned; the posterior shortening is, however, more than 
compensated by the addition of a long metasternum. That the shortening takes place 
both anteriorly and posteriorly is proved by the existence of ribs, which in the embryo 
are connected with the sternum, but which in the adult become divided therefrom and 
atrophied. ‘The cause of the shortening is “ consequent on that posterior translation 
of the shoulder-girdle which is at once expressed by the lengthening of the neck and 
the shortening of the trunk in the avian as compared with the reptilian type.” This 
sternal abbreviation is common to both Pa/wo- and Neognathe. 
In Struthio “the 7 days’ embryo shows an anterior part which may probably be 
compared to the manubrium sterni of mammals.” A study of a series of embryos shows 
that the anterior lateral processes are an outgrowth of the costal sternum ; in the Neo- 
gnathe these processes are to be regarded as vestiges of a former extension of the 
costal sternum anteriorly. 
The posterior lateral processes in the very early chick, according to Miss Lindsay, 
“consist of the ends of the primitive costal bands, preserved and prolonged for the 
attachment of the lateral part of the rectus, and subsequently modified ... to afford 
attachment to the obliquus externus.” 
These processes, as existing in the adult, may be considered a part of the meta- 
sternum, since the primitive part bears but a small proportion to the later additions. 
The metasternum, both in Struthio and Rhea, remains for the most cartilaginous 
throughout life. The cartilaginous metasternum of Dromeus and Casuarius is 
relatively somewhat smaller. 
Posterior lateral processes are wanting in the sterna of Rhea, Casuarius, and 
Dromeus. 
In Apteryx, according to Parker [71], “it appears certain that... each half of the 
sternum is not formed by the antero-posterior union of the whole of the sternal ribs.” 
{n one stage of the series which he examined the sternum apparently increased in 
length from before backwards to the level of the fourth sternal rib, which extended 
mesiad to meet it. 
The metasternum did not appear until after the posterior lateral processes had 
attained nearly their full length. In one specimen the metasternum was double, and 
