396 DISCOVERY REPORTS 



The mammary glands have been described in some detail by Lillie (191 5) for the 

 humpback (Megaptera nodosa) and further for Blue and Fin whales by Mackintosh and 

 Wheeler (1929, pp. 401-5) and Heyerdahl (1930). 



There is little to add to the descriptions of these authors. The glands on each side of 

 the body and the nipples are embraced by a compressor mammae muscle (Fig. 10 b), 

 derived from and directly continuous with the panniculus carnosus, which in the middle 

 line between the two mammae is immensely thickened and strengthened, as will shortly 

 be described. The lateral and deep fibres of this thickened part of the panniculus 

 carnosus are concerned with the posterior extremity of the mammary gland and resolve 

 themselves into two layers — one with fibres running superficial to the gland, and the 

 other with fibres running dorsal to it between the mammary gland and the fascia covering 

 the rectus abdominis muscle. The direction and superficial extent of these two layers 

 appears to be the same. The posterior fibres pass outwards and backwards and are 

 inserted upon the superficial fascia around the nipple. Farther forward the fibres pass 

 outwards transversely to the axis of the gland, and anteriorly, where they are far less 

 powerful, they are directed outwards and forwards from the middle line and are 

 inserted nearer to the inner edge of the gland, which is now separated by a considerable 

 distance from the middle line of the body on account of the oblique direction of the 

 long axis of the glands (Fig. 10). It was not found, in the foetus examined, that the 

 posterior fibres of the compressor mammae muscle both arose and were inserted, as 

 Lillie described them, in proximity to the nipple itself. 



In the foetus the gland has an oval form and is less elongated and broader in propor- 

 tion to its length than in the adult. In the 2-1 m. foetus the mammary gland was 13-5 cm. 

 in length, and at its widest point which lay half-way along its length, was 5-75 cm. wide. 



The following are the measurements of the external genitalia of a female Fin whale 

 foetus 2-i m. in length: 



Distance from the centre of the vulva to the centre of the anus 5-75 cm. 



Distance from the base of the clitoris to the centre of the anus 1 1-5 „ (approx.) 



Distance between the nipples ... ... ... ... ... 3-25 



Distance between the posterior ends of the outer pair of grooves 4-75 



Distance between the anterior ends of the outer pair of grooves 2-5 



Length of the mammary glands ... ... ... ... ... 13-5 



Greatest width ... ... ... ... ... ... ... 5-75 



MUSCULATURE 



The panniculus carnosus has the same direction and disposition as in the male sex, 

 but in the middle line, immediately anterior to the genital region, it forms a relatively 

 immense muscular mass — thicker than the similar mass in the male. The fibres of this 

 mass anteriorly are directed outwards and forwards, and posteriorly outwards and 

 backwards from a median raphe continuous with the linea alba. The deep latero- 

 posterior fibres make up the compressor mammae muscle, while the superficial ones 

 situated still more posteriorly are associated with fibres running forwards from the 



