BALB／c小鼠胸腺的发生

用ＨＥ和Ｇｉｅｍｓａ染色的鼠胚连续切片观察ＢＡＬＢ／ｃ小鼠胸腺的发生。１１ｄ鼠胚第３对咽囊内胚层与第３对鳃沟外胚层相互紧贴，组成胸腺原基，并可见淋巴细胞样细胞迁入胸腺原基。１２ｄ鼠胚鳃沟外胚层包绕咽囊内胚层。１３ｄ胚胸腺原基已形成一个实体的细胞团。原基内淋巴母细胞样细胞增多，达细胞总数的１０％左右。１５ｄ胚胸腺皮、髓质已可大致辨认，皮质内淋巴母细胞样细胞明显多于髓质。１７～１９ｄ胚胸腺的皮、髓质分

DEVELOFMENT OF THYMUS IN BALB/c MOUSE EMBRYO

he development of thymus in BAlB/c mouse embryo was examined by seriel sections ofembryos stained with HE and Giemsa stains. Day 0 of emhryonic development is determined bythe presence of a vaginal plug. On the 11th day thymus anlage is consisted of the third endoder-mal pharyngeal pouch and the third ectodermal branchial cleft contacted with each other. On the12th day the ectoderm of third branchial cleft covers the endoderm of third pharyngeal pouch.On the 13th day the thymus becomes a solid cell mass. On the 11th day lymphoblasts invade intothe thymus anlage and their number increased to about 10% of the total cell number on the 13thday. On 15th day the number of lymphoblasts in cortex is more considerable than that in medul-la. On 17 th-19th days the cortex and the medulla are distinct. The fourth endodermal pharyn-geal pouch give rise to the ultimobranchial body and do not contribute to formation of the thy-mus.