Term Name:	thymus
Synonyms:
Definition:	Paired organ where maturation of T-lymphocytes occurs. The adult thymus located on the dorsomedial aspect of the branchial cavity above the third pharyngeal cartilage. The thymus undergoes a period of rapid growth beginning at about the third week and continuing for several more weeks. Accompanying this growth is a dramatic change in the shape of the thymus. It is ovoid initially and then starts to grow dorsally along the skull, forming a characteristic protrusion. During this growth period the adult pattern of rag1-positive cortex and rag1-negative medulla becomes established. The protrusions diminish with age and the thymus gradually shrinks; at two years, the thymus is again confined to the pharynx with minimal if any protrusion.
Appears at:	Larval:Protruding-mouth (72.0h-96.0h, 3.5mm)
Evident until:	Adult (90d-730d, breeding adult)
Ontology:	Anatomy Ontology [ZFA:0001078]

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