DEVELOPMENT OF UXGULATA. 737 



whilst the respiratory process took place at the surface of contact 

 between the foetal and maternal arterial capillaries. The period 

 of gestation of the domestic Sow is about four months ; the ob- 

 served range of variation has been from 109 days to 123 days. 

 The gestation of the Hippopotamus is 234 days. The pair at the 

 Zoological Gardens at Amsterdam copulated December 1, and 

 the young one was brought forth on July 29, next following. 



Camelines and Chevrotains ( Tragulus) have the diffused con- 

 dition of the placenta as in the Mare and Sow, with some 

 minor modifications of villi and capillaries : the vitellicle, as in 

 other Ruminants, is relatively smaller than in Solipeds. The 

 urachus dilates, beyond the amnios, into a narrow cylindrical 

 sac transversely extended, or dividing into two slender cornua, 

 entering those of the uterus ; it consists of the mucous layer 

 of the allantois, is usually found collapsed, and can hardly be 

 inflated at the last month of pregnancy in the Cow. Laminated 

 deposits from the allantoic fluid are occasionally present, like 

 those called i hippomanes ' in the Mare. A much smaller pro- 

 portion of the space between amnios and chorion is thus occu- 

 pied in the Ruminants than in the Equidce, and probably other 

 Perissodactyles. 



The villi of the chorion are developed in horned Ruminants 

 on detached and limited localities, corresponding with the pro- 

 minences of the lining substance of the uterus, fig. 546, from 

 which the deciduous maternal parts of the placenta grow. The 

 surface of these caruncles, previously smooth, now buds out into 

 reticulate processes, moulding themselves upon the chorionic villi, 

 and forming cavities or canals for their inter-susception. These 

 outgrowths are homologous with the ( decidua serotina ' of other 

 Mammals, 1 but they gain a firmer texture, and usually remain 

 attached to the uterus, allowing the foetal villi to be withdrawn 

 from them at birth : they are afterwards shed, or disappear, the 

 caruncle resuming its smooth and even surface. 2 When the entire 



o 



caruncle happens to come away, it is not reproduced ; a smooth 

 cicatrix remains upon the uterine surface. 



Wherever there is placenta there is decidua. The special and 

 temporary work of developments providing capillary superficies, 

 whether on the part of the mother or foatus, being ended, they 



1 The student must not be seduced into accepting too absolutely Esehricht's dictum : 

 ' quarum alteri placenta uterina caduca, alteri non caduca est.' 



2 In xcvi', the caruncles are called ' glandular protuberances ' (p. 544) ; but it is 

 precisely on that part of the uterine lining where the utricular glands are want- 

 ing ; and the eminences and follicular depressions are peculiar to the period of 

 gestation. 



VOL. III. 3 B 



