SHOULDER-GIRDLE IN DASYURUS AND PERAMELES. 451 
Dasyurus viverrinus (Later Stage). (Pl. 41. fig. 5.) 
The larger of the two stages of the mammary fcetal Dasyure 
which I have studied has a head-length of 8mm. But though 
the foetus is so small, development has so far advanced that in 
the shoulder-girdle at least practically all the features displayed 
are those of the adult. 
The scapula (se.) has a broad blade as in the adult, with a 
well-developed spine running down near the middle of the outer 
side. The change in shape of the scapula from the narrow blade 
of the earlier stage is brought about by the remarkable manner 
in which ossification takes place. In the earlier stage, the 
only part of the scapula that is distinctly ossified is the spine, but 
ossification is just starting along the surface of the cartilage in 
the middle region. In this later stage, all the cartilage of the 
scapula, except along the upper border, the acromion process, 
and near the glenoid cavity, has been replaced by bony tissue. 
The bony development, however, has not been limited to the 
ossification of the cartilage, but has formed a moderately large 
bony plate, which passes forwards from what was the anterior 
border of the cartilaginous scapula, and has thus converted the 
narrow scapula of the early stage into the broad bony blade of 
the later. The coracoid (co.) has no longer any attachment to 
the sternum, and with the increased size of the girdle there has 
become considerable alteration in shape, so that the coracoid and 
the acromion are now mainly directly forwards. 
The clavicle is long and slender; and there is now a distinct 
omosternal cartilage (0.st.), which lies between the point of the 
sternum and the clavicle. 
The sternum (s¢.) differs in shape from that of the earlier 
stage. The presternum (p.st.), in front of the broad part which 
gives articulation to the first pair of ribs, tapers away to a rather 
slender point. 
PERAMELES OBESULA. (PI. 41. fig. 6.) 
The mammary foetus which I have examined measured 18-2 
mm, greatest length and 9 mm. head-length. At this stage, which 
roughly corresponds to the later Dasyurus stage, the coracoid has 
lost all connection with the sternum. 
The scapula is essentially similar to that of the adult. A well- 
developed spine runs down near the middle of the bone, and 
terminates in a rather broad, flat acromion, which latter, on 
