434 THE BABBIT. 



is formed by cornification of the axial or central cells of the 

 pi'ocess, while the outer or peripheral cells form the hair-sheath, 

 or follicle. The hair grows upwards from its base, and the free 

 tip soon projects above the surface of the skin. 



From the first, the hairs of the eyebrows, and of the upper 

 lip and nose are of exceptionally large size (Fig. 149) ; and one 

 particularly large hair, arising from the cheek immediately 

 below the eye, forms a prominent feature in rabbit embryos from 

 about the nineteenth day onwards, and is also very large in the 

 adult rabbit. 



2. The Claws. 



The claws are formed by cornification of the epidermis at 

 the ends of the fingers and toes. The layer of epidermis that 

 becomes converted into the claw is not, in the first instance, the 

 most superficial one, but is a special stratum, developed between 

 the superficial and the deeper or Malpighian layers of the epi- 

 dermis ; the Malpighian layer, with the underlying dermis, being 

 modified to form the bed of the claw. The distal border of the 

 claw soon projects freely at the end of the digit, and its further 

 growth is effected by additions at its hinder or attached border, 

 and to its under surface. 



3. The Mammary Glands. 



The mammary glands, like the other cutaneous glands, are 

 formed by ingrowths of the epidermis into the underlying con- 

 nective tissue. These ingrowths give off secondary branches, 

 which are at first solid, but soon become hollow, and form the 

 gland cavities ; the ducts being derived from the original epi- 

 dermal ingrowths. 



DEVELOPMENT OF THE PLACENTA. 



The placenta is the organ by which the nutrition of the 

 embryo is effected during the period of its stay in the uterus ; 

 and it is through the placenta that the mammalian embryo is 

 enabled to attain so large a size, and so high a grade of develop- 

 ment at the time of birth, although formed from an ovum of 

 extremely small size and almost devoid of food-yolk. 



The placenta (Fig. 170) is formed partly from the mother, 



