Examination of serial histologic sections of the head and neck regions of rats at selected age intervals from 14 days in utero to 100 days postnatally revealed that at 16 days in utero, a second salivary gland arises from the rudimentary parotid (Stensen's) duct. This gland develops more rapidly than the parotid gland; its acini are essentially mature prior to weaning, preceding parotid acini in this respect by several days. All cells of the secretory units of the mature gland stain positively with both alcian blue and periodic acid-Schiff, indicating that the gland is of pure mucous type. The body of the gland occupies a space lateral and mostly superior to the maxillary buccal sulcus, nestled beneath the anterior bulge of the masseter muscle, near the point where the buccal and mandibular marginal branches of the facial nerve cross paths. It is the only salivary gland in the buccal wall anterior to the third molar; hence, the proposed name of anterior buccal gland. These observations suggest: (1) Samples of rat parotid saliva collected proximally and distally to the junction of the ducts of the parotid and anterior buccal glands are likely to differ significantly in the quality and quantity of mucosubstances which they contain. (2) The divergent differentiation of two branches of the same glandular primordium in this instance implies differences in the inductive qualities of their respective mesenchymal beds.