746 ANATOMY OF VERTEBRATES. 



umbilical (allantoic) veins : the cord, as in CaUithrix, is attached 

 to the margin of the placental disc. Hapale, Nocthora, CaUithrix, 

 and other small kinds of Platyrhines are monogamous. Larger 

 platyrhine Monkeys (Mycetes, Cebus, e.g.) are polygamous: 

 three or four females are usually seen with one male. Cebus is 

 usually uniparous : the gestation is five months : the placenta 

 single, discoid, thick ; the umbilical cord with two veins and two 

 arteries: the maternal and foetal portions of the placenta are 

 expelled together, the foetal villous part does not come away 

 separately, as is sometimes the case in Lissencephala. The villous 

 and cellular structures are still more intimately blended in old- 

 world Quadrumana. In the tailed Catarhines, which, as a rule, 

 are uniparous, the placenta is double, the two being distinct and 

 apart, usually disposed upon the right and left sides of the uterus. 

 In fig. 580, where they are exposed in the green Monkey ( Cerco- 

 pithecus sabcBus) the following parts are indicate : — a peritoneal 

 coat of uterus, b b muscular coat, b' thicker portion at the cervix 

 uteri, c os tincce, d glandular rugae of cervix, e cavity between 

 cervix and decidual lining of uterus, /decidua, g chorion, h amnios, 

 i umbilical vessels associated in groups of two arteries and one 

 vein, on their way to the cord, k, k amniotic surface of the two 

 placentae, m n amniotic sheath of cord, dissected to show the 

 two arteries and one vein : o clitoris, q hair covering the labia?, 

 r diverging branches of umbilical vessels on the proximal placenta, 

 s, s vessels extending to the distal placenta t, v interplacental 

 area. In the pregnant Macacus rhesus dissected by Hunter l the 

 two placentae were contiguous, and each of more oblong form 

 than in fig. 580. The placenta shows a combined cellular and 

 filamentary villous structure. The filaments include the capillary 

 loops of the foetal vessels : but instead of lying freely in alveolar 

 cavities of the maternal placenta, they are connected or entangled 

 with the fine cellular structure which receives the blood from the 

 uterine arteries : the uterine veins have stronger and more definite 

 coats than in the human placenta : the decidua is also denser and 

 more coherent, and the layer between the uterus and placenta is 

 thicker. Each placenta consists of smaller lobes united at their 

 edges: in the fissures lie the veins, or sinuses, from which the 

 venous branches are continued. 2 



In Semnopithecus nasicus the two placentae are more remote 



than in Cercopithecus, and the distal one is smaller than that from 



which the umbilical cord is continued : this is divided into five 



lobes. Two placentae have been observed in a species of Hylobates; 



1 xciv. p. 71. ' xx. vol. v. p. 145. 



