THE DEVELOPMENT OF THE INTEGUMENTARY SYSTEM. 453 



PRACTICAL SUGGESTIONS. 



For study of the early epidermal and epitrichial layers and dermis, fix a pig embryo of 

 25 to 30 mm. in Zenker's or Bouin's fluid, cut sections in celloidin, and stain with Weigert's 

 haematoxylin and eosin (see Appendix). 



For later stages of the skin and the formation of hair follicles and papillae, cut pieces 

 from the skin and deeper tissues of a pig embryo of 5 to 6 inches and treat according to the 

 above technic, cutting sections at right angles to the surface of the skin. If the hair follicles 

 are far enough advanced, the anlagen of the sebaceous glands can be seen as buds on the 

 root sheaths. The eyelids of a human foetus of about three months afford especially good 

 material for the study of sebaceous glands. 



For early stages of the developing nails, treat the ends of the fingers and toes of a human 

 foetus of three months according to the technic given above, cutting longitudinal sections at 

 right angles to the surface of the nails. For the later stages (formation of nail substance, 

 etc.) treat the ends of the digits of an embryo of five months as above. The anlagen of the 

 sweat glands can also be seen as cylindrical growths of the epidermis into the dermis. 



The milk ridge shows very clearly in young pig embryos (20 mm. or more). Transverse 

 sections of the ridge, prepared according to the technic given in the first paragraph, are very 

 instructive, as are also sections of the mammary .glands of a new-born child. 



References for Further Study. 



BROUHA: Recherches sur les diverses phases du developpement et de 1'activite de la 

 mammelle. Arch, de Biol., T. XXI, 1905. 



BONNET, R. : Die Mammarorgane im Lichte der Ontogenie und Phylogenie. Ergebnisse 

 d. Anat. u. Entwick., Bd. II, 1892; Bd. VII, 1898. 



KALLIUS, E. : Ein Fall von Milchleiste bei einem menschlichen Embryo. Anat. Hefte, 

 Bd. VIII, 1897. 



KRAUSE, W.: Die Entwickelung der Haut und ihrer Nebenorgane. In Hertwig's 

 Handbuch d. vergleich. u. experiment. Entwickelungslehre der Wirbeltiere, Bd. II, Teil I, 1902 . 



OKAMURA, T.: Ueber die Entwickelung des Nagels beim Menschen. Arch. f. Der- 

 matol. u. Syphilol., Bd. XXV, 1900. 



PIERSOL, G. A. : Teratology. In Wood's Reference Handbook of the Medical Sciences, 

 Vol. VII, 1904. 



SCHMIDT, H.: Ueber normale Hyperthelie menschlicher Embryonen und uber die 

 erste Anlage der menschlichen Milchdriisen iiberhaupt. Morphol. Arbeiten, Bd. XVII, 1897 . 



SCHULTZE, O.: Ueber die erste Anlage des Milchdriisen Apparates. Anat. Anz., Bd. 

 VIII, 1892. 



STOHR, P.: Entwickelungsgeschichte des menschlichen Wollhaares. Anat. Hefte, 

 Bd. XXIII, 1903. 



STRAHL, H.: Die erste Entwickelung der Mammarorgane beim Menschen. VerhandL 

 d. Anat. Gesellsch., Bd. XII, 1898. 



ZANDER, R.: Bie friihesten Stadien der Nagelentwickelung und ihre Beziehungen zu 

 den Digitalnerven. Arch. f. Anat. u. Physiol., Anat. Abth., 1884. 



