PELVIS. 



161 



(/) in the Kangaroo, Phascogale, and Potoroo, 

 is not parallel with the spinal column, but 



Fig. 99. 



Pelvis of the Kangaroo, showing the marsupial bones 

 (a ) and inter-sciatic eplphysis (c). 



oblique in the opposite direction to the human 

 symphysis, so that if prolonged forwards the 

 line of direction would cut the spinal column 

 at an obtuse angle. This makes the posterior 

 opening larger in its antero-posterior diameter 

 than it otherwise would be, and allows for 

 the great encroachment of the caudal ver- 

 tebra posteriorly. The sciatic notch is long 

 and narrow, corresponding to the great length 

 of theischia ; and the foramen obturatorium is 

 large and elongated antero-posteriorly from 

 the same cause. In the Daxynrus and Pe- 

 tnunsts, the ischio-pubic symphysis is oblique 

 in the opposite direction. The antero-pos- 

 terior diameter of the anterior outlet in the 

 Kangaroo is greater than the transverse by 

 about half an inch ; but at the posterior outlet, 

 the transverse is a little greater, from the pro- 

 jection of the caudal spines before mentioned. 

 The pelvic cavity is deep in the Marsupialia, 

 and its openings are small in proportion to the 

 size of the animal, since the foetus is expelled 

 before it is full grown, and placed on the nipples 

 in the marsupial pouch to complete its deve- 

 lopment into a state of independent existence. 

 But the proportion between the pelvic open- 

 ings and the size of the foetal head, at the 

 period of expulsion, is very remote. Even in 

 the Petaurists, whose pelves are the smallest, 

 the cavity and openings are six times the size 

 of the foetal head. 



The muscles of the tail and "legs attached 

 to the pelvis are, in the Kangaroos, very 

 powerful to perform their prodigious leaps, 

 especially the gracilis and biceps. The glutei, 

 however, are not large, since the trunk is not 

 held erect on the legs by these muscles, but is 

 suspended, as it were, between the femurs, and 

 supported in front by the largely developed 

 psoae muscles, and behind by the powerful tail, 

 used as a propelling organ by the sudden 

 action of its flexor muscles. 



The pelvis of the Monotremata resembles 

 in general appearance the reptile type, although 

 Supp. 



in some other respects these curious animals, 

 especially the Ornithorhyncus, approach the 

 Birds. The sacrum of the Ornithorhyncus is 

 composed of two vertebrae, separated, as in 

 the Saurian reptiles, and placed in the line of 

 the lumbar curve, differing little in appearance 

 from the lumbar vertebras. In the Echidna 

 are three sacral vertebrae, also separated and 

 all uniting with the ilia. 



The ilia are short, thick, and prismatic, and 

 project above the spine at an angle of 140 as 

 high as the sacral spines, and presenting, in the 

 Ornithorhyncus, considerable eversion of the 

 alas, and, in a much less degree, in the Echidna 

 also. The ischia are short, bent upwards in the 

 former, and project backwards at the tuberosi- 

 ties in an angular spine, most marked in the 

 Ornithorhyncus, and giving a reptile-like ap- 

 pearance. The pubes are broad and short, 

 placed at a marked angle with the ilia, 1 10 in 

 the Echidna hystrix and 120 in the Ornitho- 

 rhyncus, and uniting by broad plate-like rami 

 with the ischial rami, which form with them 

 a long ischio-pubic symphysis. The ischio- 

 pubic plate thus formed is very like that seen 

 in the reptiles. 



The marsupial bones are also present, and 

 are very large and strong in this class, although 

 not provided with a pouch. In the Ornitho- 

 rhyncus they are broad and triangular, articu- 

 lated by the base to the whole length of the 

 pubic crest meeting in the median line, and 

 with their rounded apices directed forwards 

 and outwards. In the Echidna they are longer, 

 rounder, more pointed and less everted, with 

 two articular processes at the pubic extremity 

 (see Jig. 177. Art. Monolrcmata). 



The ilio-pectineal spines are also very large in 

 the Ornithorhyncus, and in a less degree in the 

 Echidna. The obturator foramina are small. 

 The three pelvic bones are united at the 

 cotyloids by bony union in the Ornithorhyncus. 

 In the Echidna hystrix, the union of these 

 bones is, however, effected by cartilage only, 

 and the acetabnla are perforated by a consider- 

 able opening into the pelvic cavity, constituting 

 another remarkable reptile-like peculiarity. 



Having traced the Mammalian pelvis to a 

 form presenting somewhat of the reptile tvpe 

 in the Monotremes, we may now recur back 

 to an order of animals which, from their 

 general organisation, are connected closely to 

 the order of primates, and are usually placed 

 much higher in the animal scale than the 

 position here assigned to them. 



These are the Sloths or Tardigrades, which 

 form the connecting link between \heSimiee and 

 Edentata proper. Their pelvic peculiarities, 

 however, ally them more closely to the Birds. 

 The moststrilung of these is the ossification of 

 the ilia and ischia to the broad sacrum, by 

 transformation of the sacro-iliac and sacro- 

 sciatic ligaments. We have already noticed an 

 exceptional example of this coalescence in 

 the Ruminants, in the Alcminna or pigmy 

 Chevrotain. But the pelvis of the Edentata 

 also presents a diminution of the pubic sym- 

 physis, and the absence of the ischia from 

 this junction, a separation which is carried 



M 



