268 MESSRS. B. C. A. WINDLE AND F. G. PARSONS ON [NoV. 3, 



the delamination of the gluteal mass is not nearly so complete as 

 it is in Man. In the Pig (4, 5, 8, 9, 11, 14), Ox (35, 36, 38), and 

 Sheep (41, 42, 43, 46, 47) the pyriformis is so completely fused 

 with the meso- or entogluteus that no trace of it can be found. 

 In no case does it come out of the great sciatic foramen, for this 

 is closed by a membrane, and when the muscle is distinct it rises 

 from the surface of this. The nerve-supply in the Duiker-bok 

 and Harnessed Antelope is the superior gluteal. 



Obturator internus. — ^This muscle in the Suidse (4, 8, 11, 14), 

 Tragidid* (20, 21), Giraffidse (32-34), Bovidfe (36, 39, 41, 46, 48, 

 50, 53, 54, 55), and Procaviidse (74, 75) is small, and more nearly 

 resembles a gemellus than the usual mammalian obturator in- 

 ternus : the reason for this is that the obturator tertius usurps 

 the normal origin of the muscle, and the internus has to arise 

 from the body of the ischium at the lesser sciatic notch, thus 

 reverting to what is probably the original and generalised origin. 

 Of its arrangement in the Cervidse we are not sure, but Watson 

 and Young describe it in the Elk (XXX. & XXXI.) as having the 

 usual origin from the inner side of the obturator membrane. In 

 the Perissodactyla and Elephantidse the muscle rises from the 

 inner side of the true pelvis as usual. In all cases it is inserted 

 into the bottom of the trochanteric (digital) fossa, and it is 

 supplied by a branch of the sacral plexus. 



GemellL— In those animals just mentioned in which the obtu- 

 rator internus rises at the lesser sacro-sciatic notch, the gemelli are 

 fused with it ; in the others only an inferior gemellus is as a rule 

 present. In the Horse, however (63, 65), three gemelli are often 

 met with, the third rising a little ventral and caudal to the 

 inferior, between it and the obturator externus. In the Elk (30) 

 the two gemelli are joined. 



Obturator externus and Obturator tertius (see text- figs. 25 & 26). — 

 Mivart and Murie nearly forty years ago described a miiscle in 

 Hyrax (74) passing through the obturator foramen and being 

 inserted into the trochanteric fossa with the obturator externus ; 

 this they named the obturator tertius. Later Murie found the same 

 muscle in the Giraffe (3 3), and Lesbres (Y.) has evidently noticed the 

 same thing, for he says that, in the Horse, Pig, and Ruminants, parfe 

 of the obturator internus rises from the pelvis above the obturator 

 vessels as high up as the ilium, while the other part passes through 

 the obturator foramen. We have carefully studied this muscle 

 in the Chevrotain, Ox, Sheep, Goat, Pig, Duiker-bok, Harnessed 

 Antelope, and Hyrax, and are convinced that the following is the 

 explanation of it. The obturator tertius is really a part of the 

 obturator externus, which has made its way through the obturator 

 foramen from outside, pushing the obturator membrane in front 

 of it. In doing this it has stolen a good deal of the usual origin 

 of the obturator internus and pushed that muscle out of the pelvis, 

 so that it rises, as we have shown, from the margin of the lesser 

 sciatic notch. There is, therefore, the curious paradox of the 

 obturator externus rising inside the pelvis, while the internus 



