152 T. THOMSON FLYNN 



permanently non-vascular area spoken of by Heinon and by 

 Hill. 



It should be mentioned that the posterior factor of each 

 lateral vitelline vein receives on its inner side branches from 

 the yolk-sac splanchnopleure corresponding to the fine branches 

 from the vitelline artery supplying that membrane. These pass 

 upwards in the splanchnopleure, and then continue outwards 

 into the omphalopleure to join the posterior factor as stated. 

 The measurements of the vascular area are as follows : 



Across anterior portion .... 7-5 nma. 



Across posterior portion . . . .9-9 mm. 



Greatest length, anterior portion . . 4 mm. 



Greatest length, posterior portion . . 5 mm. 



Formation of the Allantoic Placenta in 

 P e r a m e 1 e s g u n n i . 



Various stages of this are shown in figs. 13-16, 19. 



Maternal Structures. — The wall of the uterus is 

 divisible, as stated above, into two general portions, placental 

 and extra-placental regions. 



Placental Eegion . — The mucosa varies greatly in thick- 

 ness, from 0-60 to 1-1 mm., due to folds in the uterine wall. 

 The glands are numerous, long, and tortuous, measuring in 

 diameter from 0-037 to 0-051 mm. They are of the usual type, 

 being unbranched and lined by a single layer of columnar cells, 

 with deeply-staining nuclei, peripherally situated. I am not 

 able to detect any trace of the cilia which Hill and O'Donoghue 

 have observed in Perameles. The glands are in a highly 

 active state of secretion, their basal portions being filled with 

 cellular and other material. 



The inter-glandular tissue is extremely thin and tenuous, 

 but condensed where it immediately surrounds glands and 

 blood-vessels. Distributed through the connective tissue is an 

 abundance of lymph material. This is particularly evident 

 just below the uterine epithelium, in which position there is 

 a space up to 2 mm. wide filled with lymph which bathes the 

 lower surface of the uterine syncytium. Here and there this 



