OSSEOUS SYSTEM OF MAMMALIA. 99 



portion is short and contracted, compared with the ischiatic and pubic 

 portions : it varies, however, in breadth, length, and figure, in different 

 species. In many of the Insectivora the pelvis is narrow and elongated, 

 the parts composing it being slender, and the ischiatic opening very large. 

 In the genus Chrysochloris, however, this orifice is very minute, the 

 ischiatic portion being greatly developed. 



Among the Edentata in the Armadilloes, Pangolins, and Ant-eaters, 

 the iliac bones are thick, elongated, and curved slightly downward ; the 

 ischiatic bones are large, having a broad tuberosity reflected posteriorly 

 outward ; the pubic portion is considerable, and the ischiatic opening of 

 great size.* In the Sloths the iliac bones are ample, and the pelvic 

 cavity large ; in the Megatherium the iliac bones are also of great extent, 

 but the pelvic cavity is contracted ; their ample spread in the Elephant, 

 likewise, is very remarkable. Without attempting to describe the changes 

 of form and proportion, in every genus, which the bones of the pelvis 

 exhibit, the peculiar characters of this part of the osseous framework, 

 ever present, in one great group of the Mammalia, cannot be omitted. 

 The Marsupialia have two additional bones entering into the composition 

 of this part of the skeleton, which are not found in any other mammals. 

 These two bones are long, slender, and compressed, and are united, at 

 one of their extremities (spread out more than the opposite), to the pubic 

 bones, one on each side of their mutual junction, or symphisis : their office 

 is to support the abdominal muscles, and not the marsupium, or pouch, 

 of these animals ; for they are found in the males as well as females ; and, 

 in those instances, as in the Ornithorhynchus and Echidna, where no mar- 

 supium exists. The pyramidalis muscle is attached to their inner edge, 

 whence it radiates to the mesial abdominal line ; and a small transverse 

 muscle, arising from the skin on each side, passes over these bones toward 

 their upper extremity, acting as a support and compressor to them. The 

 presence of these bones (usually denominated the marsupial bones), as 

 an unvarying character in the skeleton of all the Marsupialia, is very 

 remarkable ; the more so, as they bring to mind the modification of the 

 sternum and ribs in the Saurian reptiles ; and are coincident, if not with 

 an oviparous, at least with a mode of reproduction which may be termed 

 ovo-viviparous.-j" 



Leaving, then, the pelvis, the posterior extremities next demand atten- 

 tion. As the arm consists of a humerus, fore-arm, and hand, the inferior 

 extremity is correspondingly divided into the thigh, the leg, and the foot. 

 The thigh-bone, or os femoris, in the human subject, is a large and strong 

 cylindrical bone, slightly arched backward, having a round head at its upper 



* The irregular figure of the pelvis of the Chlamyphorus will be best understood by referring to 

 the sketch of its skeleton (fig. 87). 



t Ovo-viviparous, producing young, in an egg, which is hatched internally, and previously to exclu- 

 sion by the parent. 



