The upper dilated end of the nasolacrimal duct that is lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla; it connects the lacrimal canaliculi, which drain tears from the eye's surface, and the nasolacrimal duct, which conveys this fluid into the nasal cavity; like the nasolacrimal duct, the sac is lined by stratified columnar epithelium with mucus-secreting goblet cells, and is surrounded by connective tissue. [ http://www.informatics.jax.org/accession/anna ]