490 CETACEA. 



area (PL XXXV, fig. 6) corresponding to the similar bare area in the chorion of 

 Orcella, &g. There may, or may not, be a corresponding bald area on the uterus, 

 but if present it is very feebly developed. The villi of the chorion are much larger 

 and more crowded together on the right than on the left horn, which is the exact 

 opposite of what has been described by Turner in the chorion of the Narwhal. 

 They are most numerous and attain their greatest size on its posterior or umbilical 

 area, and are least developed on its anterior aspect. The whole surface is studded 

 over with them with the exception of certain bare patches, and they have a distinct 

 tendency to arrange themselves in wavy ridges on the more rugose portions and in 

 rounded clusters on the areas where they are less developed. 



Plate XXXVII, figures 12 and 13, ]*espectively show a vertical section through 

 the chorion at a bare spot (bj with the partially injected villi on each side, and a 

 surface view of the chorion also partially injected, the tufted villi in this case 

 surrounding the middle bare spot. 



Smooth spots of Chorion (PI. XXXV, figs. 7 and 8). — The whole surface of the 

 chorion is covered with small circular smooth spots (PL XXXV, fig. 7) and with 

 others bearing very fine rugosities or folds, such patches being devoid of villi and 

 varying in size, but corresponding to the smooth spots of the uterine mucous mem- 

 brane (fig. 9) to which they would appear to be opposed. They are best seen on 

 the anterior, ventral and dorsal walls of the left horn, i.e., where the vilh are sparse. 

 They vary in size from 0*06 to 0*25 inch in diameter, and are irregular in form. In a 

 square inch of some regions, as many as eighteen to twenty such spots may be counted. 

 A bare patch of a special character occurs on the left pole of the left horn of the 

 chorion. It forms a crescentic linear bare area at the pole, the horns of the crescent 

 having an interval of an inch between them, and from the concavity of the crescent 

 a very narrow linear area extends towards the pole. This smooth area corresponds 

 to the mouth of the Eallopian tube (PL XXXI, fig. 3). There is no other bare area 

 on the pole of the right horn, its apex being covered with villi. But it must be 

 borne in mind that this portion of the chorion (figs. 2 and 3) being neither distended 

 with amnionic nor allantoic fluid lies comparatively loose in the Eallopian end of the 

 right horn. The extremity, however, of the short uterine pouch (PL XXXIV, fig. 2 

 sp. and fig. 3) is perfectly devoid of villi as in Orca^ for about an inch in extent, and 

 this bare area corresponds to the os uteri internum (PL XXXI, fig. 2). 



The most characteristic bare surface of this chorion (PL XXXV, ^^. 1), 

 however, is a long narrow linear area on that side of the funis which lies towards 

 the dorsum of the mother. It stretches from within 5 inches of the left to 

 within 17 inches of the right pole of the chorion, having thus an extension 

 of 19-50 inches in a straight line and a serpentine course of 25-75 inches. Opposite 

 the umbilical attachment it attains a breadth of about 0' 50 inch, rapidly diminishing 

 in diameter on either side of this to 0'06 inch. Erom the left it passes on to the 

 right horn, running for some way along the dorsal wall of the latter and following 

 the course of the larger vessels. 



' Turner : Lectures on Placent., p. 43, fig, 7. 



