MCERITIIEKIUM. 
119 
continues back the long' nxis of the ilium. Where this hone forms the outer 
houndary of the obturator foramen it is trihedral, hut ])osteriorly it flattens out into 
a broad and comparatively thin plate, of which the upper outer angle {tuber ischit) 
is very prominent [is.t.). The posterior border is somewhat convex. Internally the 
hone 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 peculiar interest of this pelvis lies in its great resemblance to that recently 
figured by Abel * as belonging to the Sirenian, Eotheriimi mgyptiaeum, 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 ilium, the 
same greatly expanded ischium, and an acetabulum of almost exactly similar form. 
Unfortunately, in no specimen of the pelvis of Meeritlierium is the pubis well 
preserved, hut it w^as clearly comparatively thin and w'eak. 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 Eotheriuin ; 
(2) the position of the fossa for the attachment of the rectus femoris muscle is a 
little different ; (3) the obturator 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 Moeritherium 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 lai'ge 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 Ilalitherium (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, wliile the terrestrial, probably swamp-loving, 
Moeritherium retains the more primitive type of pelvis, which, by the widening of tlie 
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 (PI. XL fig. 8, h.) is large, rounded, and pedirnculate ; 
its posterior surface bears a deep pit for the ligamentum teres {l.t.)', it is separated 
* O. Abel, “ Die Sirenen der mediterrauen Tertiiirbildungen Oesterreichs,” Abbaudluagen der k.-k. 
geologiscbeu lieichsanstalt, vol. xis. pt. 2, pi. vii. fig. 1 (Vienna, 1904). 
