a nipple or teat;the small projection of a mammary gland 奶头; 乳头
noun [专属名词]乳头；乳头状隆起物；疣
birds were much similar with other bird species, which were outer layer, spongy layer, cone layer, mammilla, shell membrane layer. 鸟类与其他鸟类物种的结构非常相似，其结构包括外层、海绵层、锥体层、乳头层和壳膜层。
