HELLO,

Clavicle can be considered as a modified long bone as :

1. It is the only long bone positioned horizontally and is subcutaneous throughout.
2. Has no Medullary Cavity(Grays Anatomy mentions medial 2/3 has medullary cavity).
3. Clavicle is the first bone to begin ossification and last bone to complete ossification.
4. It is the only long bone which ossifies by two primary centers.It ossifies mostly in membrane but long bone mostly ossify in cartilage.