Complex sentence: The Subscapularis is a large triangular muscle which fills the subscapular fossa, and arises from its medial two-thirds and from the lower two-thirds of the groove on the axillary border of the bone.
Split into simpler sentences: The Subscapularis is a large triangular muscle which fills the subscapular fossa. It arises from its medial two-thirds and from the lower two-thirds of the groove on the axillary border of the bone.