AbstractDevelopment of the arterial vasculature in the secondary palate was studied in Sprague‐Dawley rat fetuses treated with vitamin A plus cortisone, 6‐aminonicotinamide (6‐AN), and X‐rays. Most of the control and teratogen‐treated fetuses were India‐ink injected for study of the palatine vasculature; others were histologically sectioned in the coronal plane. All 3 teratogens affected development of the lateral palatine processes and arterial vasculature. Vitamin A plus cortisone produced severe palate deformities. The palatine processes were composed of multiple horizontal and vertical processes containing abnormal epithelial and cartilaginous components. The palatine arteries remained widely separated in the maxillary area of the palate but narrowed to form a “V” pattern in the premaxillary area. 6‐AN and X‐rays delayed development of arterial patterns and the palatine processes, and decreased growth of the lateral palatine processes. After reorientation the palatine arteries remained fairly widely separated in fetuse