222 MR. W. P. PYCRAFT ON THE MORPHOLOGY AND 
sterni, near the middle of its extent (fig. 4c), is an area of bone conspicuous on 
account of its thinness. Now it seems more than probable that these thin areas are 
the last traces of a once deep fissure which has gradually closed up, thus uniting to 
the body of the sternum a pair of posterior lateral processes. Parker has noticed a 
similar indication of the closure of these fissures in Apteryz. 
Fusion probably first took place, in the case of Rhea, between the free ends of the 
processes and the mesosternum by syndesmosis of the membrane, by which the fissure is 
invariably closed. A slight expansion of the free ends of the processes and metasternum, 
such as is indicated in Tinamid@, would materially hasten this process of closing. It 
is also to be noted that the membrane closing this fissure is generally thicker posteriorly 
than anteriorly ; this also would contribute towards the work of obliteration. If, once 
again, we imagine these fissures open, the resemblance between the sternum of hea 
and Crypturi will be found to be significantly striking. 
It has been already suggested by Gadow that the protuberantia sterni may represent 
a degenerate keel. This seems quite probable. Seen in profile its keel-like resemblance 
is quite as close as that claimed for Apterya by Parker (fig. 4p). The sternal callosity 
so conspicuous in the living bird is represented amongst the Meognathe in Opistho- 
comus and is a quite secondary character. 
b. The Pectoral Arch. 
The shoulder-girdle of the flightless Palwognathe has undergone considerable 
modification and bears evidence throughout of retrogression. The coracoid and scapula 
are no longer free, except in the very young bird, but completely anchylosed, forming, 
the one with the other, a very obtuse angle, instead of an acute angle as in modern 
birds. 
In Dromeus the sternal (epi-coracoid) border of the coracoid, though wide, is less than 
the length of the whole coracoid. Only the inner half of this border is received within 
the coracoid grooves ; its outer portion is free and underlies the anterior-lateral process. 
The pro-coracoid is ligamentous. The supra-coracoid foramen is large and receives 
several pneumatic apertures. 
The scapula is slender, and looks like an outward, upward, and backward outgrowth 
of the coracoid. It bears a strongly marked articular facet for the vestigial furcula. 
The pectoral arch of Dromeus ater does not appear to differ materially from that of 
D. nove-hollandie. I gather this from a sketch by Dr. Henri P. Gervais, kindly 
made for me at the request of Prof. Oustalet, to whom I am much indebted, as 
well as to Dr. Gervais. 
The following measurements (in millim.) accompanied the sketch of Dr. Gervais :— 
Length from pro-coracoid process to tip of scapula 
Greatestlengtht of coracoidy viycssstee/1..seve 2 saee ceeeece tes seecee 0:062 
Wadthyyepi-corecoid reriones.s,. chee. ene ne ee 0:047 
