The clavicles, when united, as usual, form the furcula; mostly the distal median portion is drawn out into a hypocleidium of various shape.
In birds of various groups the clavicles are more or less degenerated, the reduction beginning at the distal end.
In none of the existing, and in but few of the extinct types, are collar-bones, or clavicles, developed; and the scaphoid and lunar bones of the carpus are separate.
These rodents are characterized by the imperfectly rooted cheek-teeth, imperfect clavicles or collar-bones, cleft upper lip, rudimentary first front-toes, smooth soles, six teats and many cranial characters.
- Amphicoelous; parietals separate; clavicles dilated and with a perforation near the ventral end.