FOETAL NUTRITION: THE PLACENTA 411 



Carnivora. — The Carnivora are characterised by a zonary 

 form of deciduate placenta. The following account of its 

 development refers particularly to the dog and cat, which have 

 been most frequently investigated. The gestation period in 

 the cat is about sixty-three days, and in the dog fifty-eight to 

 sixty-two days. In both the ovum takes a comparatively long 

 time to traverse the oviduct. On reaching the uterus the 

 blastocyst is covered by a thick prochorion which prevents 

 adhesion for a considerable period. 



The mucosa is matured, as in Ungulates, at the first pro- 

 oestrum by the development of a well-difEerentiated sub- 

 epithehal cellular layer, and of the glands and crypts (see p. 398). 

 The crypts provide an increase of superficies and of secreting 

 epithelium, and are later concerned in the attachment of the 

 ovum. They have been recognised by aU the authorities with 

 the exception of Robinson, '^ who states that he can find no 

 evidence that any of the crypts are other than the ducts of the 

 uterine glands. At the first and each succeeding procestrum 

 there is a marked hypersemia of the mucosa, and from the 

 rupture of some of the superficial capillaries mihary haemorrhages 

 occur (see Chap. III.). 



At the beginning of pregnancy, blood effusions are found 

 close under the surface of the mucous membrane, but bleeding 

 into the uterine cavity, which took place during the prooestrum, 

 has entirely ceased. The epithelium of the surface glands and 

 crypts is swollen and pervaded with minute fat-globules in the 

 dog (Bonnet ^) and cat (Mehssenos ^). The glands widen 

 quickly into " chambers," and tracts of their prohferated 

 epithehum are invaginated, and often obUterate the lumen. 

 The widening of the glands and crypts makes the deep layer 

 spongy. The capillaries increase and form practically the 

 whole of the sub-epithehal layer. Immediately below it hes 

 the layer of glandular ducts which are obhterated by debris 



^ Eobinson, Hunterian Lectures, Jour, of Anat. and Phys., vol. xxxviii., 

 1904. 



^ Bonnet, "Beitrage zur Embryologie des Hundes,'' Anat. Hefte, vol. xx., 

 1902. 



" Melissenos, "Ueber die Fettkornchen und ihre Bedeutung In der 

 Placenta bei den Nagern und der Katze," Arch. f. mikr. Anat., vol. Ixvii., 

 1906. 



