DEVELOI'MEXT oh' THE FlETUS. 101 



In the third month, the hairs are perceptible on the fcetus of the 

 Mare and Cow. Hair folhcles have been observed in embryos of the 

 Pig which did not measure more than two inches in length. They first 

 appear about the eyebrows, lips, and joints of the limbs, and the whole 

 of the body is covered at the sixth or seventh month ; they are usually 

 observed in the fa'tus of the Mare and Cow around the lips, towards 

 the eighteenth week of gestation. The hair may be shed and renewed 

 before birth, for it has been found in the amniotic fluid and in the 

 stomach of the fcctus. Each hair is developed in a prolongation of the 

 epidermic layer which is imbedded in the substance of the derm ; this 

 prolongation is constituted by a bottle-shaped mass of cells. In the 

 centre the cells are modified and heaped up, so as to form a small cone 

 whose base covers the growing papilla ; this cone elongates, until it 

 touches the superficies of the epidermis, when it becomes bent in the 

 effort to push itself through, but, finally, it issues beyond the surface, 

 where it may grow freely. 



The sebaceous and pcrspiraiorji glands are developed in a similar 

 manner, at the middle period of uterine life. The horny productions, 

 such as the claws, lioo/s, enjots, and cJicsniits, are apparent at an early 

 stage. Towards the end of the second month there can be perceived in 

 the foetus of the Cow, at the extremity of each digit, a small, pale, and 

 transparent conical tubercle ; this is the rudiment of the claw. The 

 hoofs of Solipeds appear towards the twelfth week, and about the com- 

 mencement of the fourth month they are more developed ; their texture 

 has become firm and opaque, whereas before it was gelatinous and 

 transparent, and has assumed a fine yellow tint. They are always 

 soft, however, until birth, in order to guarantee the integrity of tlie 

 fa'tal envelopes. At mid-term, brown or black patches appear, if the 

 coronet is pi-ovided with pigmentary stains ; but it is not until about 

 the end of gestation that the horn begins to show the greenish tint 

 proper to it when destitute of pigment ; though the remainder of this 

 production, particularly its lower part, preserves its yellow colour until 

 the young animal is born. In Solipeds the chesnuts are seen at mid- 

 term, in the form of thin brownish plates, which soon become darker. 

 The structure of the hoof is not tubular until after birth, when, the 

 fa^al hoof gradually disappearing, the horn that replaces it is fibrous 

 and tubular, and much more consistent. 



The corneous substance is developed at the expense of the blastema 

 which the capillaries of the modified derm throw out on its surface. 

 In this material appear nucleated cells which, pressing against each 

 other, become at first polygonal in shape and flattened, then lose their 

 nucleus and are confounded with each other. At a later period, cells 

 of a new formation are moulded on the papilhc of the coronary cushion 

 and plantar surface of the foot of Solipeds and Ruminants, giving it that 

 fibrous appearance which is so striking during extra-uterine life. 



The Loconwtorij Apparatus. 



The development of bone, and with it the locomotory apparatus in 

 general, next demands our attention. Bone is developed in the blastema 

 or primitive basis — a transparent glairy mucous matter containing 

 numerous minute corpuscles. This progressively acquires increased 

 firmness, sometimes assuming a membranous or ligamentous condition, 

 usually of a gristly consistence before its conversion into bone. The 

 change into cartilage is denoted by the appearance of minute nucleated 



