482 Proceedings of Boy al Society of Edinburgh. [sess. 
On the Development and Morphology of the Marsupial 
Shoulder-Girdle. By R. Broom, M.D., B.Sc. Com- 
municated by Sir William Turner. 
(Read January 9, 1899.) 
{Abstract.) 
An examination is made of a series of early stages in the 
development of the shoulder-girdle in the common Phalanger 
( Tricliosurus vuljpecida ), and of early stages in the development of 
that of the Bing-tailed Phalanger (Pseudochirus peregrinus), and 
of the Bock-wallaby ( Petrogale penicillata). Though in their 
main features there is much similarity between the girdles of the 
different genera, there are certain peculiar features in each. 
In a Trichosurus foetus of 8'5 mm., though the main part of 
the scapula is chondrified, together with the glenoid portion of the 
coracoid and a portion of the acromion, the rest of the arch, the 
sternum, and the greater part of the clavicle, are still mesenchy- 
matous. The coracoid can be traced downwards as a fan-like 
expansion, which meets the first rib and the sternum. Between 
the coracoid and the clavicle a feebly-developed thin sheet 
apparently represents the precoracoid (epicoracoid). The clavicle 
is partly ossified at its upper part, and it is very manifest that 
there is no cartilaginous basis. 
In the Trichosurus foetus, at birth (14 mm.), the scapula is well 
developed. The acromion is a large process which springs from 
the anterior border of the blade. The spine is not yet formed, 
though its basis can be distinctly traced as a membranous structure 
stretching from the acromion upwards along the outer side of the 
scapula in its anterior third* There is no cartilaginous basis for 
this part of the spine. The coracoid is of large size, and its lower 
part, which is somewhat bulbous, articulates with the sternum and 
with the first rib. 
In the later development it is shown that the girdle becomes 
detached from the sternum, owing to degeneration of a portion of 
