39 8 DISCOVERY REPORTS 



levator ani in the great fibrous mass at the sides of the vulva. There is a great muscular 

 pad also, with fibres directed transversely, between the vulva and the anus. This thick 

 transverse sheet consists largely of the levator ani muscle in its deeper part (Fig. n). 

 In front, immediately dorsal to the hinder lip of the vulva, the transverse mass of fibres 

 incorporates the "interpelvic ligament" of Struthers, which is more developed in the 

 female than in the male. A thick transverse sheet of fibres is thus formed, running 

 dorsally between the labia majora, making a half sphincter round the posterior side of 

 the vulvar opening (Fig. u). As already mentioned, at the sides of the vulva are two 

 large fibrous masses which receive fibres from the panniculus carnosus and the levator 

 ani. Thus the labia majora can evidently be strongly drawn together, so as to compress 



the vulva. 



In this connection one may recall that within its musculo-fibrous body the vulva 



narrows very rapidly, forming a funnel-shaped aperture with tough corrugated sides 



(Fig. 1 1 e). In the adult there is a hard fibrous pad with a corrugated surface bounding 



the genital opening anteriorly within the vulva. The sides and posterior face of the 



genital aperture are provided with the muscular and fibrous masses above referred to, 



the action of which is to constrict the opening. Immediately within the narrowest part 



of the funnel-like genital opening there is a circular constrictor muscle (Fig. n/) 



surrounding the lower limit of the vagina. This muscle is the sphincter vaginae and is 



homologous with the bulbo-cavernosus muscle of the male. It has been described by 



most previous authors, notably Meek (1918) and Murie (1873). Of this muscle in 



Globicephala melaena Murie wrote (p. 289): "It is attached to the vagina near the 



anterior end of the pelvic bone and, as a broad fleshy mass, encircles the generative 



canal beneath the mammary gland. Broadest in front it narrows behind and becomes 



inserted upon the strong median fascia posterior to the vulva." In Balaenoptera its 



arrangement seems to be the same as in Globicephala. Ventrally, beneath the vagina, the 



muscle is a strong sphincteric band ; dorsally it thins out upon the vaginal wall and 



becomes incorporated with the fibrous masses already described in that position. It 



seems evident from the anatomy of the parts that the female takes a very active part in 



the act of coition and that the erected penis is very firmly gripped by the female. This 



process is carried out by means of the fibrous structures within the walls of the vulva 



and in the labia majora and of the sphincter vaginae muscle. The fleshy tags around 



the genital opening and the rugae on its walls prevent the vulva, already lubricated 



by the secretion of mucus, from slipping upon the smooth surface of the penis. The 



grip is probably maintained until the female orgasm is complete and the structures 



relax. 



The description already given of the rectus abdominis, ischio-caudalis and hypaxial 

 muscles of the male applies equally to these muscles in the female. The levator ani, 

 however, is larger and more powerful in the female than in the male and takes part in 

 the formation of the fibrous mass around the vulva. 



The ischio-cavernosus or erector clitoridis muscles (Fig. 11 g) are a pair of stout bands 

 arising from the ischial portions of the pelvic bones. In Phocaena phocaena Meek (1918) 



