PLATANISTA. 



495 



ridge of the back, and these remain a long time persistent. Besides these folds 

 the skin generally is covered with wavy, transverse wrinkles, which however 

 disappear in adult age in a healthy dolphin. The upper surface of the snout 

 (PL XXXI, fig. 1, p.) is covered by scattered, rather strong, palish yellow bristles, 

 and the under surface of the lower jaw with twenty-six similar hairs. I have not 

 been able to detect hairs in any other part of the body and there is no whisker or 



Fig. 18. 





J\ ■"^i '*' 



A sketch of the extended penis (p) and cut umbilical cord (u) of the foetus of Platanista. Drawn of 



natural size. 



moustache as occurs on the foetus of Ptound-headed Dolphins. In the specimen 

 specially under consideration, which is a male, the long tubular extremity of the 

 urethral tube (fig. 18) is exserted, and the tip of the double glans is visible, the 

 foreskin embracing these parts being bent with them to the left side. 



Mechanism of Farturition. — The arrangement I have described, in whatever 

 horn the foetus may be, although it is probable that conception generally takes 

 place in the left horn, doubtless plays an imj)ortant part in parturition. The partu- 

 rient contractions of the septal fold of the left horn must be very powerful 

 and by violently constricting the membranes in its neighbourhood it must hasten 

 their rupture. This accomplished, its after contractions across the wedge-like 

 posterior portion of the body of the foetus force the latter to the left side of the left 

 horn, a course which is rendered imperative owing to the sejatal fold being placed 

 to the right of the pectoral fins which would be liable to be driven outwards at 

 right angles to the body against the septal fold, and thus seriously retard birth. 

 The common septum must also, from its oblique position, prevent the straightening 

 of the caudal portion of the foetus, and moreover by its contractions it must assist 

 in driving the foetus to the left, in the first instance. As the foetus so passes, and 

 as at each contraction it is held in the grasp of the septal fold of the left horn, 

 the tail begins to straighten as the snout curves round to pass from left to right in 

 the progress of the young animal out of the left horn towards the common cavity 

 of the uterus. In this cavity strangulation of the snout in the orifice of the right 

 horn is obviated by the close apposition of the folds which guard it. 



