288 DR. J. MURIE ON THE ORGANIZATION OF THE CAAING WHALE. 
The sphincter ani consists of a circlet of coarse, strong, fleshy fibres, the true external 
sphincter; but there are, besides, circular fibres more deeply placed around the gut, 
which would represent a sphincter ani internus (vide fig. 48). 
The rectus abdominis, which I have already described, partly mingles with the 
generative muscles, inasmuch as its posterior narrowed extremity and terminal tendon 
enclasp the deeper fleshy structures of the vulva and winds round each innominate 
bone, finally being inserted in the neighbourhood of the chevron bones. 
What I assume to be the counterpart of an ischio-coccygeus is a thick and strong 
muscle which, with its fellow of the opposite moiety, constitutes a crescent-shaped 
perineal mass. Each muscle arises by narrow but somewhat strong tendon from the 
surface of the middle of the os innominatum. Passing backwards and inwards, its fleshy 
fibres expand and are inserted into the perineal raphe, and join those of the levator 
and sphincter ani. It is a retractor of the pelvic bone when the perineal attachment 
is the fixed point; reversely it may assist the levator ani. There is a likelihood also 
that after pregnancy, when the mammary gland is enlarged, it may exert pressure on 
that organ during lactation. 
The erector clitoridis, or ischio-cavernosus, is a large diagonally placed fleshy band of 
muscle, of nearly equal breadth throughout. It lies partially beneath the last and 
between it and the rectus abdominis, with the compressor mammz and gland to its 
inner sides. Before the positions of the parts are disturbed this muscle has a more cur- 
vilinear aspect than the deeper dissections (figs. 77, 78) warrant. It has an extensive 
origin from the surface of the posterior moiety of the innominatum bone, at least 
2 inches, as also from the fibro-cartilage and broad pelvic fascia. With a direction 
forwards and inwards, it lies upon the sphincter vagine, and is ultimately inserted into 
the median line. In male Cetaceans the muscle corresponding to this is a very powerful 
one, with a great pelvic attachment, and stretching on to the side of the root of the 
penis. 
Alongside and mesially from the erector clitoridis is a somewhat fusiform, moderate- 
sized, or, indeed, compared with the last, small-sized muscle. Its office I take to be 
chiefly a compressor of the mammary gland, as such I name it; for it constitutes a semi- 
circle round and partially over that organ. Its attachment posteriorly is beneath the 
ischio-coccygeus, from the strong perineal fascia in front of the rectum. From this the 
muscle, sweeping outwards, forwards, and then inwards, or embracing the mammary 
glands as a semilune, narrows anteriorly, and is fixed upon the strong fascia before and 
partially at the side of the mamme’. 
Besides the two foregoing, two other muscles lie between them and the border of 
the rectus abdominis. ‘The first, in proximity to the erector clitoridis, is a short and 
laterally compressed slip. Inwardly it is fastened to the median strong fascia of the 
1 Geoff. St.-Hilaire, ‘ Annales,’ 1834, p. 183, alludes to a muscular covering of the mamme, which, he thinks, 
presses upon the gland like the pouch of the Kangaroo. 
