**Question:** Pinna develops from -

A. Ectoderm
B. Endoderm
C. Mesoderm
D. Neural crest cells

**Core Concept:** During embryonic development, various cell layers contribute to the formation of different parts of the body, including the external ear. In the case of the pinna (the visible part of the ear), its development involves contributions from specific cell layers.

**Why the Correct Answer is Right:** The pinna primarily develops from the ectoderm, which is one of the three primary germ layers in early embryonic development. The ectoderm contributes to the formation of the skin, nerves, and sensory organs, including the ear. Additionally, neural crest cells also play a role in the development of the pinna, contributing to the formation of the cartilage and connective tissue.

**Why Each Wrong Option is Incorrect:**

A. Endoderm: Endoderm is responsible for the development of the respiratory, digestive, and urinary systems, not the pinna.
B. Mesoderm: Mesoderm contributes to the development of the skeletal system, muscles, and blood vessels, not the pinna.
D. Neural crest cells: While neural crest cells are involved in the development of the pinna, ectoderm is the primary source responsible for the pinna's formation.

**Clinical Pearl / High-Yield Fact:** A better understanding of ear development is crucial for understanding congenital anomalies, such as microtia, a condition characterized by underdeveloped or absent pinna. This knowledge can guide clinical diagnosis and management of such cases.

**Correct Answer:** A. Ectoderm