MCEEITHEEIUM. 119 



continueis back the long axis of the ilium. Where this bone forms the outer 

 boundary of the obturator foramen it is trihedral, but posteriorly it flattens out into 

 a broad and comparatively thin plate, of which the upper outer angle {tuber ischii) 

 is very prominent (is.t.). The posterior border is somewhat convex. Internally the 

 bone is produced into a process forming the posterior boundary of the obturator 

 foramen, and so thin that in no specimen does it remain unbroken, so that nothing, 

 is known as to the form and extent of the symphysis. 



The pecuUar interest of this pelvis lies in its great resemblance to that recently 

 figured by Abel* as belonging to the Sirenian, Eotherium cegyptiacum, Owen 

 (text-fig. 68, C), a species occurring in the somewhat earlier white limestone of the 

 Mokattam Hills. In this pelvis there is the same straight and narrow ihum, the 

 same greatly expanded ischium, and an acetabulum of almost exactly similar form. 

 Unfortunately, in no specimen of the pelvis of Mosritherium is the pubis well 

 preserved, but it was clearly comparatively thin and weak. The chief differences 

 between the two pelves seem to be : (1) so far as can be ascertained from Abel's 

 figure and description, the sacral surface is less distinctly developed in Uotherium ; 

 (2) the position of the fossa for the attachment of the rectus femoris muscle is a 

 little different ; (3) the oibturator foramen is rounder in Eotherium. Nevertheless, the 

 similarity of the two pelves is such that if that described by Abel is without doubt 

 Sirenian (and it seems highly improbable that it is anything else), then it may 

 fairly be suggested that Mosritherium and Eotherium, both occurring in the same 

 region (the one the most primitive Proboscidean, the other occupying the same position 

 with regard to the Sirenia), are in fact closely related, and had a common ancestor 

 in early Tertiary times, probably in the Lower Eocene. It is interesting to note 

 that the acetabulum of Eotherium indicates the presence of a large functional femur,, 

 so that the animal must have been less exclusively aquatic than the later Sirenia. 

 Furthermore, in the rather later beds in which the remains of Moeritherium are 

 found there is a Sirenian Eosiren, in which the pelvis (text-fig. 68, B) is already 

 almost as much reduced as in the later Halitherium (text-fig. 68, A) ; the adoption 

 of a completely aquatic life having apparently led to a very rapid reduction of the- 

 pelvis and hind limb through disuse, while the terrestrial, probably swamp-loving,. 

 Mosritherium retains the more primitive type of pelvis, which, by the widening of the- 

 gluteal and pelvic surfaces, and the consequent lengthening of the crista ilii, became 

 the broad pelvis of the larger Proboscideans. 



The head of the femur (PL XI. fig. 8, h.) is large, rounded, and pedunculate ; 

 its posterior surface bears a deep pit for the ligamentum teres {l.t.); it is separated 



* O. Abel, "^Die Sirenen der mediterranen Tertiarbildungen Oesterreichs," Abhandlungea der k,-k.. 

 geologischen Eeichsanstalt, vol. lix. pt. 2, pi. viL fig, 1 (Vienna,. 1904), 



