470 CHORDATA. 
longer protrudes from the surface as a “tail” but may 
even occasionally become fused to the sacrum. 
Tue Lime-GirDLEs.—The girdle of the fore-limb or 
pectoral arch closely approximates to the reptilian type in 
the Afonotremata, but becomes more specialised in the 
Marsupialia and Eutheria. 
In the Monotremata the coracoids are large and meet 
the sternum. They bear on their inner border a pair of 
precoracoids. There is also a T-shaped episternum. In 
the Metatheria and Eutheria the coracoids atrophy, as also 
the precoracoids. Amongst other vestiges of these bones 
there is a process upon the. scapula, the coracoid process, 
which is said to be the distal end of the precoracoid, the 
true coracoid being represented by a small bone taking part 
in the formation of the glenoid cavity. 
Hence in nearly all mam- 
Fig. 324.—THREE TyPEs OF mals the scapula alone is 
MAMMALIAN SCAPULA. left to bear the fore-limb, 
Cee especially as in a great num- 
ber the clavicle atrophies. 
The scapula is correspond- 
ingly highly developed. It 
is a large, triangular-shaped, 
flattened bone, with a bony 
ridge down its outer surface 
called the spzme, terminating 
ot z in a free process, the acro- 
A, Cursorial. _B, Aquatic or natatorial. heal Me which the distal end 
ae "C, ‘Arboreal. ‘of the clavicle is attached, 
when present. 
In the running types (Ungulata), in which the limb has 
little diversity of movement, the clavicles go and the scapula 
is long and tapering, with short suprascapular border. In 
the climbing types (Primates), with varied movements of 
the forelimb, the scapula is an approximation to an equi- 
lateral triangle. whilst in the swimming types (whales, seals) 
the scapula is broadened out, shortened lengthwise, with 
long suprascapular border. The spine is pushed forwards, 
so that the postscapular fossa is very large and the pre- 
scapular fossa is small. 
