umbilical allantoic) veins: the cord, as in Callithrix, is attached to the margin of the placental disc. Hapale, Nocthora, Callithrix, 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 fœtal 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 oldworld 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 (Cercopithecus sabaus) the following parts are indicate:-a peritoneal coat of uterus, b b muscular coat, b' thicker portion at the cervix uteri, e os tincæ, d glandular rugæ of cervix, e cavity between cervix and decidual lining of uterus, ƒ 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 placentæ, 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 In the pregnant Macacus rhesus dissected by Hunter' the two placenta 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 fœtal 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

area.

In Semnopithecus nasicus the two placentæ 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 placenta have been observed in a species of Hylobates: xx. vol. v. p. 145.

1

XCIV. p. 71.

2

but in the Chimpanzee the placenta is single. In all old-world Quadrumana the umbilical vein is single, as in Bimana. Where any trace of vitellicle has been detected in Quadrumana, it has been very small.

§ 406. Development of Bimana.-The lining substance of the

human uterus, when an ovum is impregnated, augments in thickness, fig. 570, and seems to degenerate into a pulpy spongy mass, into which the ovum sinks on entering the womb: its position is shown, diagrammatically, in fig. 572, B, e: but the special chamber in which, at first, it lies loosely, is exhibited in fig. 581: here, bristles are introduced at the orifices corresponding with those of the oviducts, and pass out at the beginning of the cervix uteri,

umbilical (allantoic) veins: the cord, as in Callithrix, is attac to the margin of the placental disc. Hapale, Nocthora, Callithr: and other small kinds of Platyrhines are monogamous. Larg platyrhine Monkeys (Mycetes, Cebus, e.g.) are polygamous three or four females are usually seen with one male. Cebu's usually uniparous: the gestation is five months: the place single, discoid, thick; the umbilical cord with two veins and tw arteries: the maternal and fœtal portions of the placenta are expelled together, the foetal villous part does not come away separately, as is sometimes the case in Lissencephala. The villon and cellular structures are still more intimately blended in olaworld 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 (Cerc pithecus sabaus) the following parts are indicate:-a peritoneal coat of uterus, b b muscular coat, b' thicker portion at the cervix uteri, e os tinca, d glandular rugæ of cervix, e cavity between cervix and decidual lining of uterus, ƒ 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 placentæ, m n amniotic sheath of cord, dissected to show the two arteries and one vein: o clitoris, q hair covering the labiæ, r diverging branches of umbilical vessels on the proximal placents, s, s vessels extending to the distal placenta t, v interplacental area. In the pregnant Macacus rhesus dissected by Hunter1 the two placenta 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 placenta 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 placentæ have been observed in a species of Hylobates: xx. vol. v. p. 145.

1

XCIV. p. 71.

2

out in the Chimpanzee the placenta is single. In all old-world Quadrumuna the umbilical vein is single, as in Bimana. Where any trace of vitellicle has been detected in Quadrumana, it has been very small.

§ 406. Development of Bimana.-The lining substance of the

human uterus, when an ovum is impregnated, augments in thickness, fig. 570, and seems to degenerate into a pulpy spongy mass, into which the ovum sinks on entering the womb: its position is shown, diagrammatically, in fig. 572, B, e: but the special chamber in which, at first, it lies loosely, is exhibited in fig. 581: here, bristles are introduced at the orifices corresponding with those of the oviducts, and pass out at the beginning of the cervix uteri,

where the decidua ends. The utricular canals become dilated and tortuous, and are still lined (or formed) by epithelial cells: but formifaction is active in the production of diverse defined corpuscles from the 'granule' up to the colossal fibre-cells,' fig. 416. At the fourth or fifth month the decidua becomes condensed to

Decidual lining substance of human uterus, shed in

a thinner layer, and detached from the muscular wall of the A uterus by a new, soft deposit, which takes on the utricular character of the original lining substance, and remains after parturition.

The primary changes of the impregnated human ovum have not been observed. It cannot be doubted that the germ-mass is due to the cleayage process. Whether the outer coat continues to be the hyalinion when the ovum passes into its deciduous nest; whether the hyalinion then gives place to an expanded 'animal' layer of the blasto

derm; or whether this be superseded by the vascular layer of the allantois-are conjectural possibilities suggested by observed facts in lower Mammals, and awaiting proof. This is certain, that when the amnion is completed, the intestine formed, and the vacancy of the ventral walls contracted to an umbilicus, the remnant of the vitellicle is reduced to a crumpled yellowish subcircular corpuscle, 1 line in diameter, adherent to the outside of the amnion, and connected with the intestine by a long filamentary omphalo-mesenteric pedicle, accompanied by a vitelline vein and arteries. The vascular layer of the allantois has formed, or organised, the chorion: its unvascular layer is disposed like a serous membrane between the amnion and chorion, and maintains a connection for a time with a filamentary urachus, expanding within the pelvis into a urinary bladder. The growing ovum pushes the free wall of its decidual chamber into the uterine cavity (traversed by the bristles in fig. 581), and, filling it, reduces it to a narrow hydroperionic space.' The layer of decidua so pushed in seems to be reflected upon the ovum, and is termed decidua reflexa' or decidua ovuli': the thicker layer lining the womb is the decidua

6