1885.] The “Collar Bone” in the Mammatia. 1175 
mounds, and the narrow, flexible tongue securing the food, stand 
in place of the burrowing habit, thus bringing the shoulder joint 
under much less active conditions. In the South American 
armadillos, which are mote omnivorous and are “ diggers,” the 
clavicles are developed. The “ pangolins,” scaly covered ani- 
mals, mainly terrestrial and rolling themselves in a ball on the 
approach ôf danger, have no clavicles. 
In the order Rodentia we find all the Sciuromorph group with 
fully developed clavicles ; the squirrels are either arboreal or bur- 
rowers; the marmots, Arctomyine, are typical burrowers, while 
the beaver, though eminently aquatic, brings the fore limbs into 
active use in the construction of its dams and lodges. 
The Myomorpha (rats, mice, gophers, etc., typical gnawers 
and diggers) have well developed clavicles, the gnawing habit 
bringing the fore limbs and shoulder girdle actively into use to 
steady the head and neck and the object which is being worked 
upon. 
_ In the Hystricomorpha (porcupines, cavies, etc.) clavicles are 
found developed in the climbing tree-porcupines (Sphingurinz), of 
which our Canadian species (Erethizon) is a member, and absent 
in the large African porcupine and all others of the Hystricine 
group, which is strictly terrestrial but not fossorial. 
The chinchillas have well developed clavicles, the horse-trip- 
ping burrows of the “ Pampas Viscacha” being too well known 
to the riders of that region. The agoutis (Dasyproctidz), inhab- 
iting the banks of streams in the South American forests, semi- 
aquatic and sub-ungulate (¢. e., having the feet partially encased 
in a horny sheath or hoof) have rudimentary clavicles. The | 
Caviide (guinea pigs) and the “capybara,” the largest living 
rodent, semi-aquatic, with webbed. feet, have imperfect clavicles, 
« The Lagomorpha consists of two living families, the Lagomyi- 
dz, small burrowing animals called “picas,” inhabiting Alpine 
regions, and the Leporidz (hares and rabbits) ; the former family 
having well developed, the latter rudimentary clavicles. The 
hares are typical runners, solitary, never burrowing, depending 
for safety in speed and making their characteristic “form”; the 
species known as the rabbit, however, differs largely in habits 
_ from the other members of the family, being more or less gre- 
garious, living in “ warrens” which it burrows out, and having 
much less capacity for speed. Clavicles are developed in both; 
VOL. XIX.—NO. XIT, 77 
