这个词是什么意思？
An epithelial outgrowth of the cloaca in birds similar to the thymus in mammals. It atrophies within 6 months after birth and remains as a fibrous remnant in adult birds. It is composed of lymphoid tissue and prior to involution, is the site of B-lymphocyte maturation.
中文名称索引；定义为 MeSH 英文原文，尚未逐条译审。MESH:D002060 · MeSH 2026。
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