368 H. H. SWINNERTON. 
but does not yet meet its fellow of the opposite side. For 
the greater part of its length it is in contact with the 
cleithrum. ; 
The most striking feature at this stage is the great length 
of the postcoracoid process, which rivals even the pre- 
coracoid process. It is interesting to note that this process 
forms a posterior continuation of the cartilage bordering the 
glenoid line. 
Stage IV (figs. 6 and 7).—The pectoral skeleton now 
bears a close resemblance to that of the adult, and differs 
from the previous stages chiefly in the orientation of parts. 
Whilst the scapular region still retains an upright position, 
the coracoid region, and with it the fin, has rotated inwards 
into an almost horizontal position (fig. 6). Consequently the 
glenoid line, which has hitherto been parallel to the long 
axis of the body, now slopes obliquely backwards and in- 
wards towards this axis. This change was foreshadowed in 
Stage II], when the hinder part of the fin-plate faced 
slightly posteriorly. 
The fin-plate has now broken up completely into the four 
radials indicated in Stage III. These are now rod-like, and 
increase in length from the pre-axial to the post-axial 
element. At its distal end each bears a pair of distal radials 
—mere nodules of cartilage. These increase in size in a 
reverse direction, viz. from post- to pre-axial border, a fact 
which suggests that the first formed radial element also 
belongs to the distal series. In support of this it may be 
pointed out that like the other distal radials it appears before 
the radials themselves ; that it is not in the same line with 
the latter, but with the former; and finally that, like all the 
distal elements, it is enclosed by the base of the dermal 
fin-ray. oh, 
The scapular region has now, for the first time, risen above 
the pre-axial corner of the fin skeleton, which is thus removed 
some distance from the cleithrum (cf., figs. 4 and 7). | 
The coracoid region has extended still further forward, so 
