爪

爪（Claw），又稱爪子或鉤爪，是羊膜动物（哺乳類、鳥類及爬蟲類）於手指及腳趾末端的表皮角質層附加物。

参考资料 
 Maddin & al. (2009): The anatomy and development of the claws ofXenopus laevis (Lissamphibia: Anura) reveal alternate pathways of structural evolution in the integument of tetrapods. Journal of Anatomy, no 214 (4): pp 607-19 Abstract 

動物解剖學