Anatomy of finfish and shellfish

Unit 9 - Endocrine system

9.2.7. Thymus
In the actinopterygian fishes a rather massive thymus is observed in the medial wall of the branchial cavity.this thymns apparently arises from contributions of several of the branchial pouches.the thymus of Latimeria is a comparable to that of the actinopterygian but is lobular.in the cyclostomes all of the gill pouches give rise to thymus tissue dorsally.the anterior pouches also have ventral anlagen. In the adult only the dorsal parts remain.