AND THE FOETAT; MEMBRANES, TX TEE rHK'K. 353 



fho longitudinal extent of the fold depends on the length of tlie sero- 

 araniotic connection. The form and extension of such a fold, vary 

 greatly, however, in different individuals and at different stages. 

 One instance of great development is given in Fig. 37, and its sections 

 in Figs. 91-93. The planes of these sections are indicated by dotted 

 lines in Fig. 37; in wliich the points, A, B, and C, on the dotted line 

 marked 92, correspond t(^ the points marked hy the same letters in 

 Fig. 9l^ It is not clear what significance this fold has. 



At both extremities of the sero-amniotic connection the amnion 

 is also slightly folded longitudinally (Diag. 6) ; transverse sections 

 oi" such folds are represented in Fig. (i(S (at the anterior end) and Fig. 

 ()9 (at the ])Osterior end). Tn these figui'es, above the general am nicotic 

 ca^ ity there appears a second smaller cavity marked Amu. A reference 

 to Diag. (i will show that this appearance is due to the folds. How- 

 ever, these transverse and lonor-itiidiiial folds, beinçf disturbed bv the 

 oTowth «^f the amnion as well as [)v the chano-es of the sero-amniotic 

 connection itself, become insignificant after the first week of the 

 incubation. 



These temporary effects upon the amnion are, however, fol- 

 lowed by others much more important on the allantois and also on 

 the albumen-sac. The albumen-sac of certain birds, and the yolk 

 sac of the chick have been studied by Duval ^ and recently by A^irchow," 

 but knowledge of the general development of the foetal membranes of 

 the chick is still left very imperfect. Hence, it may not be superfluous 

 to give here a l:>rief outline (^f the development of the foetal membi'anes 



1. M. Duval : Études histologiques et morphologiques sur les Annexes des Embryons 

 d'Oiseau. Journ. de L'Anat. et de la Physiol., XX. 1884. 



2. H. "^^irchow : Der Dottersack des Huhnes. Internationale Beiträge zur Wissenschaft- 

 lichen Medizin. Bd. 1. I regret that I know this article only by extracts given in Ergeb- 

 nisse der Anat. u. Entwickl. (1892 ; Wiesbaden), and Zoologischer Jahresbericht 7.ur 1891 

 (I89b; Berlin). 



