PELVIS 



163 



parts, evidently in the position of the sacro- 

 sciatic ligaments (</). The ischia (c) are 

 comparatively short and directed obliquely 

 backwards and downwards, and have remark- 

 ably slender tuberosities, as is the general cha- 

 racteristic of the Sloths. The inferior rami 

 (Jc) slope much forwards, and join with the 

 pnbis in a plate of bone (//) before reaching the 

 symphysis (/), which is very narrow and 

 formed by the pubes only. The pubes (b) of 

 the Mylodon are long and very slender, and 

 form an angle of about 160 with the ilia, the 

 apex of the angle being directed forwards, a 

 remarkable peculiarity, by which it differs, in 

 common with the Ant-eaters, from the other 

 Mammalia. The vertebra-iliac angle is rather 

 acute, being about 12o, and the ilio-ischial is as 

 small as 120, being very near the human angle. 



Pelvis of the Mylodon robitstus, posterior view ; show- 

 ing the ossification of the sacro-iliac and sciatic 

 ligaments. 



The whole pelvis is remarkable for its 

 breadth and shallowness. The anterior outlet 

 is of an oval form, with the long diameters 

 antero-posterior. The posterior opening is 

 somewhat pentagonal, and, from the great 

 antero-posterior direction of the ischial rami 

 and the ossified sacro-sciatic junction, pre- 

 sents a flat level rim. The sacro-sciatic fora- 

 men (/) is comparatively small, but the obtu- 

 rator foramen (o) is large and oval. 



The pelvis is one of the most characteristic 

 parts of the fossil Megatherium, as forming 

 the fulcrum of muscular forces of unusual 

 vigour. The sacrum is very narrow, and shorter 

 proportionably than in the Mylodon, and is 

 composed of five vertebra?, only the last being 

 broader transversely. There is no ankylosis 

 to the last lumbar vertebra. 



The iliac wings are large and expanded, 

 with a concavity directed forwards, the ante- 

 rior superior spines overhanging the femurs, 

 and the external border very concave. They 

 are more massy than in the Myladon, and 

 present no hook-like process on the crest. 

 The iscltia are broad, blade-like, and massy ; 

 the tuberosities are not well marked, but 

 rounded anil ankylosed to the lower sacral 



vertebrae, enclosing a small foramen, and 

 contributing, with the ankylosed ilia, to sup- 

 port the weight of the animal. Ilio-ischial 

 angle 125. The pnbes are slender and very 

 oblique, and form, like the Mylodon, a reversed 

 ilio-pubic angle of about 155. The pubic 

 symphysis is narrow, and presents anteriorly 

 a rostrated projection. The acetabula are 

 large and near to each other ; the planes are 

 inclined from the perpendicular about 65. 

 The anterior outlet is oval, with long diameter 

 antero-posterior. The posterior has the long 

 diameter transverse. The obturator opening 

 is comparatively small. The whole pelvis 

 has a very massive appearance. 



The pelvis of the other Edentata presents 

 the same general type as that of the Sloths. 



In the Armadillo (Dasi/pus longicaudus] there 

 is a sacrum of nine vertebrae, the three upper 

 of which are ankylosed to the ilia, and the 

 sacral spines are coalesced in a crest. The 

 sacrum is narrowed to a remarkable extent 

 between its iliac and its sciatic portions, ex- 

 panding much in the latter part to meet and 

 coalesce with the ischia, with which it forms a 

 broad osseous plate in the site of the sacro- 

 sciatic ligaments. The oblique sacro-iliac ridge 

 is also well marked- The caudal bones are 

 numerous. 



The ilia are long, strong, broad, and pris- 

 matic, and the a\x are prolonged into broad 

 lamellar plates, which are ankylosed con- 

 tinously to the sacrum, and assist to support 

 the carapace. The ilia are much more ap- 

 proximated to each other than the ischia. 

 Lumbo-iliac angle 155. The ischia are large, 

 broad, and considerably divergent, with broad 

 tuberosities prolonged dorsallyto support the 

 shell ; coalescing in a broad plate with the 

 lower sacral pieces, and enclosing a moderately 

 sized sacro-sciatic foramen. The rami are at 

 right angles to the body of the ischia. The 

 ilio-ischial angle is marked, (14-5). The pubes 

 are slender and very obliquely directed back- 

 wards, making an ilio-pubic angle of 150; 

 and the symphysis is short, especially in the 

 Weasel-headed Armadillo, in which also the 

 ilio-pubic angle is smaller. (130). The pos- 

 terior pelvic outlet is much larger than the 

 anterior, from the greater eversion of the ischia. 

 In the Cape Ant-eater (fig. 102.) the sacrum 

 is composed of six pieces, with the spines () 

 coalesced, but leaving foramina between them, 

 and the last transverse processes (Z>) elongated. 

 Caudal bones numerous (fig- 102.). 



The ilia are very thick and prismatic, and 

 more perpendicular to the spine, with the an- 

 terior and posterior borders thickened into a 

 strong ridge. The alae are concave externally, 

 the posterior superior spines (c] prolonged 

 dorsally, and ankylosed to the sacrum, and the 

 anterior superior (g), prolonged and curved 

 outwards and downwards. The ischia are 

 very long, expanding into a broad plate poste- 

 riorly (c), but do not touch the last sacral 

 vertebra. The ischial spines (i) are marked, 

 and the tuberosities present two tubercular 

 projections, one directed outwards, long and 

 sharp () ; and the other thicker, and directed 



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