**Core Concept:** The frontonasal duct is a developmental structure that forms during embryonic development and eventually regresses. In normal embryology, the frontonasal duct connects the nasal pit to the anterior nasal spine and serves as the precursor to the nasal bones, lacrimal gland, and part of the frontal process of the maxilla.

**Why the Correct Answer is Right:** In normal embryology, the frontonasal duct regresses and is absorbed. As a result, it does not persist into adulthood. The correct answer is **A**. In this case, the frontonasal duct would not be present and would not have a designated opening.

**Why Each Wrong Option is Incorrect:**

A. The frontonasal duct should not open into the nasal cavity (Option A). In normal development, it should not be present.

B. The frontonasal duct does not open into the lacrimal gland or anterior nasal spine (Options B and C). These structures are derived from different developmental pathways.

D. Regression of the frontonasal duct occurs in normal embryogenesis, so it should not be present in adults (Option D).

**Clinical Pearl / High-Yield Fact:** Understanding the normal embryonic development of the frontonasal duct is essential for recognizing malformations, such as Pfeiffer syndrome, which is characterized by fusion of the nasal bones, hypoplastic nasal bones, and other craniofacial abnormalities. Recognizing these malformations can help guide the diagnosis and appropriate management of these patients.