()-\ THE FOETAL MEMJJKA.NE« OF CUELOXJA. -io 



;iiiiiii()tic <'()iiiiccTi(jii, thus piNjduciii^' ;i (lee]» incision in its oiitliiu'. 

 riie postcfini- ((»list I'ictitjii OWL'S its orii^'iii to tljis circuiiistaiKX'. niid 

 llms liL'twt'cii tlic mid.lle. and the left. IoIk' there is always interposed 

 tlie sei'o-aniiiiot ic coimeetion. There ;ire some details of" tin's poste- 

 ri(.)r (j(jnst rietion wlndi lam not altle to imderstand. The allantois 

 [irepares to meet the sero-aniniotie eonneetion. sometime before it 

 reaches in its lirowtli the latter struetnrc (/. c, before there is, so fai- as 

 I see, any mechanical necessity for a consti'iction) by folcbni^- itself 

 and pi'odncinii' a constriction. Thus in Tig. G 7 îhe apex of the 

 [)osterior const I'iction is some distance from the remnant of I lie 

 posterioi' tube <»f the amnion (which marks the ])()sterior end <>f the 

 sero-amniotic connection), and is nnu'ked by fohfs of the allantois 

 slioAvinu' tliemselves as wln'te streaks. The result of this is that in 

 later stau'es (Fi.i;'. VJ^) the jnjsterior ctjnst rictioii is. near its head, 

 divided into two liml)S : one contains the sci-o-anniiotic connection 

 and its termination, the remnant of the jjosteritir tube of the amnion, 

 and the othei' is simj)lv an incision in the margin of the allantoic 

 vesicle. In still later stages, the latter is much the deeper of the two 

 aïid becomes (juite <;ons])icuous (ligs. (ÎS and 71. Tl. \ III.). I am 

 unable to see an\' nei^essity for tlie existence of this incision. 1 can 

 not detect anv one large bloo<l-ve^seJ or set of blood-vessels, wliich 

 might cause it, as the anterior constriction of the allantois is caused 

 by the right set of allantoic vessels. It aj)pears t() be a congenitally 

 acquired character. 



The nearl\' circular shape of the middle lobe is produced ])y iVie 

 fact tliat if is necessarily limited in its gi'uwth l.»_y the sero-amniotic 

 connection which obstructs its front. In fict it is the right and left 

 allantoic lobes that grow to cover the larger part of tlie yolk-sac. 



The right and middle lobes are suj)plied mostly by \\n' I'iglit set 

 «•f bl(H)d-vessels. while the left IoIjc is sn[)plied by the left set. 



