BREEDINa. 27 



is not included in the amnion. The placenta, or after-birth, is 

 a soft, flat, spongy, highly vascular body. It assumes a variety 

 of forms in the various classes of animals. In the mare and sow 

 it is diffused — /. e., it consists of villi scattered over nearly the 

 whole of the outer surface of the chorion, and received into 

 crypts or corresponding recesses in the uterine mucous mem- 

 brane. In the ruminant the placental villi are collected into 

 groups, forming a number of rounded or ovoid objects, termed 

 cotyledons. It is the medium of communication between the 

 mother and foal, its office being to supply necessary nutrient to 

 the fetus. In carnivora the villi are collected in a mass, which 

 assumes the form of a belt, surrounding the chorion, and hence 

 called a zonary placenta. In rodentia the placenta is discoid, the 

 villi being assembled in a more or less circular mass. 



THE UMBILICAL CORD. 



The umbilical cord is the channel of communication between 

 the fetus and the placenta. It is composed of two arteries and 

 one vein. 



DEVELOPMENT OF THE FETUS. 



The horse's embryo at six weeks has a length of 1 3-5 inches; 

 at seven weeks, 2 inches, and at eight weeks, 2 3-5 inches; the 

 thoracic and abdominal cavities are closed. At the ninth week 

 the embryo measures 3 1-5 inches; the external ears are very 

 small; the Wolffian body, genital glands, and suprarenal cap- 

 sules are present. At ten weeks the embryo measures 3 4-5 

 inches; the internal and external genital organs are formed. At 

 eleven weeks the embryo measures 4 1-5 inches, and at twelve 

 weeks 5 3-5 inches. At seventeen weeks it measures 14 3-5 

 inches. At seventeen weeks the first hair appears on the lips. 

 At twenty-two weeks the lips, eyelids, and point of the tail are 

 provided with hair. The length of the embryo at tlie twenty- 

 third to twenty-fourth week is about 27 inches. The hair ap- 

 pears on the crest and back. The testicles lie near the abdominal 



