FCETAL MKMBKANES OF CHIROMYS MADAGASCARIENSIS. 1153 



we term it, of the chorionic sac that occupied the light horn of the 

 uterus. Upon its surface the chorionic folds reach their maximum 

 (as in specimen A), and display strongly marked secondary folds 

 and convolutions (PI. lY. figs. 7, 8, & 9). Elsewhere upon this 

 face of the chorion, and more particularly opposite the head of the 

 fcetus, the folds are relatively weak, and form low ridges separated 

 by wide smooth areas ; similar bare places also occur opposite 

 the postero-dorsal aspect of the foatus. 



In comparison with the condition of the chorion in other 

 Madagascar Lemurs, the strong lamination of the appendage 

 that occupies the right (non-foetal) horn of the uterus is worthy 

 of notice, This prolongation of the chorionic sac may be absent 

 even at near full term (Anthony, 12, p. 247, Propithexus), and 

 apparently, as a rule, enters the non-foetal horn only as pregnancy 

 advances (Turner, 5, pp. 578, 587; Anthony, 12, p. 247), and 

 is normally less strongly laminated than other pai'ts of the sac. 



2. AUaniois. 



The allantois, as in other Lemurs, is a voluminous and 

 characteristically lobulated organ whose cavity, though extensive 

 in the circumferential plane, is flattened radially between the 

 chorion with which its outer wall is fused and the amnion which 

 is fused with its inner wall. Between the entodermal lining of 

 the allantoic sac and the trophoblast of the chorion is situated a 

 layer of delicate fibi^illar connective tissue, formed from the 

 all ante- chorionic mesenchyme and prolonged to form the axes of 

 the villous folds. In it run the numerous branches and factors 

 of the allantoic arteries and vein on their way to and from the 

 subtrophoblastic capillary plexus, presently to be described. 



The allantois consists of a main lobe, into which the allantoic 

 canal opens and which accordingly represents the primitive 

 allantoic vesicle, and of a number of accessory lobes of irregular 

 shape, which have grown out from the primary sac and approach 

 one another across the rump and back of the foetus. In 

 specimen A the relations of the main sac and its various 

 lobes to the underlying foetus were asceitained by carefully 

 dissecting away the chorion. Two views of the preparation * 

 so made are shown in PI. II. figs. 2 and 3 (cf. also text- 

 figs. 2 & 3), representing the left and right sides respectively of 

 the fcetus. 



The main lobe (partially opened in text-figs. 2 & 3 and PI. II. 

 figs. 2 & 3) lies upon the left side of the posterior trunk region of 

 the fcetus, and extends across the ventral surface some little way 

 beyond the mid-line on to the right side, covering the feet and 

 tail. It communicates with the allantoic canal, which runs 

 down in the umbilical cord, by a small slit-like aperture, situated 

 opposite the gap between the left knee and elbow. 



* R. Coll. Surgeons Museum, Plij'siol. Series, No. 3582.52. 



