1) Lacking a breastbone 2) Unconnected 
• (a.) Not sternal; -- said of ribs which do not join the sternum.
(a-stur´nәl) not joined to the sternum. pertaining to asternia.
A·ster'nal adjective [ Prefix a- not + sternal .] (Anat.) Not sternal; -- said of ribs which do not join the sternum. 
Type: Term Pronunciation: ā-ster′năl Definitions: 1. Not related to or connected with the sternum, asternal rib. 2. Without a sternum.
[adj] - (anatomy) not connected to the sternum or breastbone
adjective not connected to the sternum or breastbone; `asternal ribs`
not reaching to or connected with the sternum.