File:Bailey356.jpg

Fig. 356. Vertical section through the anlage of the mammary gland of a human foetus of 16 cm

Bonnet.

In embryos of six to seven mm., or even less, a thickening of the epidermis occurs in a narrow zone along the ventro-lateral surface of the body (Strahl). In embryos of 15 mm. this thickening, known as the milk ridge, extends from the upper extremity to the inguinal region (Kallius, Schmidt). Later the caudal end of the ridge disappears, while the cephalic portion becomes more prominent. The further history of the ridge has not been traced, but in embryos considerably older the anlage of each gland is a circular thickening of the epidermis in the thoracic region, projecting into the underlying dermis. It seems most probable that this local thickening represents a portion of the original ridge, the remainder having disappeared.

Later the central cells of the epidermal mass become cornified and are cast off, leaving a depression in the skin (Fig. 356). In embryos of 250 mm. a number of solid secondary buds have grown out (Fig. 357). These resemble the anlagen of the sweat glands, to which they are generally considered as closely allied (Hertwig, Wiedersheim and others), and represent the excretory ducts. Continued evaginations from the terminal parts of the excretory ducts form the lobular ducts and acini. The acini, however, are scarcely demonstrable in the male, and not even in the female until pregnancy. Lumina appear by a separation and breaking down of the central cells of the ducts and acini, the peripheral cells remaining as their lining.

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Reference

Bailey FR. and Miller AM. Text-Book of Embryology (1921) New York: William Wood and Co.

Cite this page: Hill, M.A. (2024, April 19) Embryology Bailey356.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Bailey356.jpg

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