430 HARRIS HAWTHORNE WILDER ON 
THE APPENDICULAR SKELETON. 
Shoulder Girdle. 
The shoulder girdle consists of a pair of thin plates, almost entirely cartilaginous, 
wrapped about the sides of the body near the anterior end of the trunk, and entirely dis- 
connected from other parts of the body skeleton and from one another. At about the 
middle of each plate is situated the glenoid fossa for the reception of the head of the 
humerus, and from this as a center there radiate three processes or lobes, one extending 
dorsally and two ventrally. The dorsal or scapular extension is narrow at its origin but 
broadens out towards its free end into a hatchet-shaped piece which extends as far dor- 
sally as the transverse processes of the vertebrae. The narrow part of this extension 
becomes ossified to form a scapula, in shape something like the diaphysis of a shaft bone, 
with a constricted middle portion and two broadened ends; beyond this ossification the 
hatchet-shaped piece remains as a cartilaginous suprascapula. Of the two ventral exten- 
sions, the anterior, or procoracoid, is long and narrow and directed nearly anteriorly, while 
the posterior, or coracoid, forms an almost circular flat plate closely applied to the myo- 
tomic muscles on the ventral side of the thoracic region and extends so far beyond the 
median line that the coracoid of one side considerably overlaps the other, the left being 
usually the ventral or superficial one. 
The cartilage, which is thin in most regions, is considerably thickened about the 
glenoid fossa both to strengthen the region and to allow sufficient depth for the reception 
of the head of the humerus. Externally, the thickened portion forms a definite ridge or 
lip nearly surrounding the fossa, being deficient only for a small space upon the antero- 
medial aspect. 
Midway between the glenoid fossa and the re-entrant angle formed between procor- 
acoid and coracoid is seen a small foramen coracoideum through which passes the supra- 
coracoid nerve on its way to supply the muscles upon the ventral surface of the shoulder 
girdle. C.K. Hoffmann has pointed out that in the Anura this nerve lies in the interval 
between the procoracoid and coracoid, while here it bores through the cartilage, and that 
the result is brought about in the former case by a deepening of the incision between the 
two elements in question far enough to include the region of the foramen. 
When the shoulder girdle is in its proper relationship to the body, the coracoid 
extends from the second to the fourth myocomma, and hence the largest of the sternebra, 
the one connected with the fourth myocomma, is situated exactly at the point at which 
the posterior margins of the two coracoids diverge from one another, a relation precisely 
similar to that of the sternal plate of the higher Urodela and of the arciferous Anura (e. ¢., 
