532 EMBRYOLOGY. 



2. At the deep end of the hair-germ the vascular hair-papilla 

 is begun by a growth of connective tissue. 



3. The epithelial hair-germ is differentiated into : 



(a) A young hair, by the cornification of a part of the cells ; 



(b) An actively growing cell-layer situated between the shaft 



of the hair and the papilla, the bulb, which fur- 

 nishes the material for the growth of the hair ; 



(c) The outer and the inner sheaths of the root. 



4. Around the epithelial part of the fundament of the hair 

 there is formed from the surrounding connective tissue the hair- 

 follicle. 



5. The nails in Man and the claws in other Mammals are de- 

 veloped from a dorsal fundament the nail-plate and a ventral 

 fundament the plantar horn. 



6. The plantar horn in Man is reduced to the nail-welt. 



7. The thin nail-plate which is formed at first is for a time 

 covered with a layer of cornified cells, the eponychium, which in 

 Man is shed in the fifth month. 



8. The milk-gland is a complex of alveolar glands. 



9. At first there arises a thickening of the mucous layer of the 

 epidermis, which is converted into the glandular area that is after- 

 wards marked off from the surrounding parts by a wall and becomes 

 somewhat depressed. 



10. From the bottom of the glandular area there grow forth in 

 great numbers the fundaments of alveolar glands. 



11. After birth the glandular area, embracing the excretory 

 ducts of the glands, is elevated above the surface of the skin, and 

 converted into the nipple and the areola mammfe. 



12. After birth there is a transitory secretion of a small quantity 

 of milk-like fluid the witches' milk. 



LITERATURE. 



(1) Development of tJie Nervous System. 



Ahlborn. Ueber die Bedeutung der Zirbeldriise. Zeitschr. f. wiss. Zoologie. 



Bd. XL. 1884. 

 Altmann, R. Bemerkungen zur Hensen'schen Hypothese von der Nerven- 



entstehung. Archiv f. Anat. u. Physiol. PLysiol. Abth. 1885. 

 Balfour. On the Development of the Spinal Nerves in Elasmobranch Fishes. 



Philos. Trans. Kov. Soc. London. Vol. CLXVI. 1876. 



