ON THE ARRANGEMENT OF THE F03TAL MEMBRANES IN THE CETACEA. 483 



The urachus freely communicated at its abdominal end with the bladder. 

 At the angle, where the umbilical vessels diverged from each other, the urachus 

 rapidly expanded into a huge funnel-shaped sac-like allantois, capable of hold- 

 ing several pints of fluid. When the allantois reached the chorion, it became 

 prolonged both to the right and left in the form of a comparatively wide, almost 

 cylindrical sac-like horn (fig. 7, b, b). The left horn-like prolongation extended 

 to 7 inches from the end of the left horn of the chorion, where it formed a 

 cul-de-sac. The right horn-like prolongation entered the right cornu, but did 

 not reach to within 21 inches of the tip of the right horn of the chorion. By far 

 the greater part of the attached surface of the allantois was in contact with the 

 amnion. But, at the points where the umbilical vessels reached the chorion, 

 opposite to the abdominal aspect of the foetus, the allantois came in contact 

 with the deeper layer of that membrane, to which it continued to be attached 

 by a limited portion of its surface, as far as the ends of its horn-like prolonga- 

 tions. The free surface of the allantois was perfectly smooth, and was bathed 

 by the allantoic fluid. 



Explanation of Diagrams. — Outline diagrams to show the arrangement of the membranes at the stage of develop- 

 ment described in the text. A, Longitudinal section. B, Transverse section. E, Embryo, ch, Chorion, al, Allantois. 

 am, Amnion represented in a dotted line. The umbilical vesicle is not shown. 



The amnion formed a continuous bag from one horn of the chorion to the 

 other, but was not co-equal with it in extent. For though in the left horn it 

 reached to 2 inches from the pole of the chorion, in the right the chorion 

 extended 9 inches beyond the closed end of the amnion (fig. 13 c, c). Where 

 the amnion was in relation to the dorsal aspect of the foetus, it was connected 

 by a delicate filamentous tissue to the inner layer of the chorion ; but, where 

 the allantois was attached to the chorion, i.e., opposite the abdominal aspect, 

 the amnion was reflected on to the outer surface of the cylindrical horns 

 and funnel-shaped sac of the allantois, and was conducted by that membrane 

 to the umbilical cord, which it invested. Beyond the closed ends of the 



filled ; that others were injected with a carmine-coloured gelatine from branches of the umbilical vein 

 only, when both the extra and intra-villous capillaries were readily filled ; and that others again were 

 injected both from artery and vein, untd the coloured gelatines intermingled in the capillaries, and 

 produced there a purple tint. 



VOL. XXVI. PART II. • 6 K 



