PELVIS. 



159 



panded than the shaft in most of the order. 

 They form with the spine an angle of about 



Fig. 98. 



Pelvis of the Hare, anterior view. 



165 in the Hare, and 150 in the Porcupine. 

 In the Copyrus, Rats, Mice, and Guinea-pig, 

 they are nearly parallel with the spine ; but in 

 the Jerboa they cross the spine at an angle 

 much less than in others, being about 140. 

 In the Jerboa the iliac wings are curved out- 

 wards superiorly and projected much on the 

 dorsum of the spine, reaching beyond the 

 elongated spines of the last lumbar vertebra. 

 The ilia of the Beaver, and, in a less degree, in 

 the Hare, are expanded, with prolonged and 

 irregularly curved crests (c), a little everted 

 at the spinous processes (g), and propor- 

 tionally short in the shaft. The ischia in 

 Rodents are generally long, especially in the 

 Beaver and Jerboa: In the latter animal they 

 are directed much outwards, with tuberosities 

 large, much expanded, and everted posteriorly, 

 to give firm attachment to the strong sacro- 

 sciatic ligaments. They are placed in a right 

 line with the ilia, the ilio-ischial angle being 

 wanting as in the Carnivora (see fig. 112. 8.). 

 In the Hare the tuberosities of the ischia are 

 large, and present well-marked lateral pro- 

 cesses (c\ which are'everted, and rise above the 

 level of the coccygeal vertebrae. The pubes are 

 long and slender, and generally join with the 

 ischia in a long median symphysis projecting 

 in a sharp, anterior, vertical, ridge (/); except 

 in the Porcupines, Rats, and Mice, which 

 have a short symphysis pubis. In the Jerboa 

 there is a slight pubic spinous process, very 

 externally placed ; this is better marked in 

 Hares (rf), Rabbits, and Beavers. The ilio- 

 pubie angle in Hares and Rabbits is about 

 120 to 130. In the Jerboa it is more oblique, 

 145 ; and still more so in Rats and Mice, 150. 



The sciatic notch is generally long and nar- 

 row, especially in the Jerboa; and the obturator 

 foramen very large, particularly in the Beaver. 

 The pelvic cavity and outlets are large and 

 capacious, especially in the Jerboa, in which, by 

 the outward direction of the ischia, the poste- 

 rior outlet is much larger than the anterior. In 

 the Beaver also the transverse pelvic diameter 

 is large, and separates widely the hinder ex- 

 tremities of these animals, to aid their swim- 

 ming habits. In the Capybara however, the 

 pelvis is of little capacity. 



In the Guinea-pig it is compressed so much 

 laterally, that the anterior opening is of a 

 triangular shape, with the apex at the pubic 

 symphysis. According to Le Gallois, it 

 measures only 11 millimetres transversely 

 in a full-grown female, while the foetal head 

 measures 20 millimetres across. Three 

 weeks before labour begins, the elastic liga- 

 ment uniting the symphysis pubis becomes 

 thick, soft, and moveable ; and eight to ten 

 days before, the pubes, turning on the sacro- 

 iliac joints as on a hinge, begin to separate 

 rapidly, till the time of parturition, when 

 they admit one or two fingers between 

 them. After accouchment, the symphysis 

 quickly returns to its original condition, and 

 in a few days presents only a little thick- 

 ness and mobility, the process being delayed 

 only by age and sickness. Le Gallois found 

 the sacro-iliac symphysis also very moveable, 

 so as to allow of the retreat of the sacrum, 

 and the increase of distance between its ex- 

 tremity and the pubic symphysis when the 

 foetal head pressed upon it. In this manner 

 the pelvis of the Guinea-pig is widened, 

 during labour, in all its diameters. Its young 

 are produced in a very advanced state of de- 

 velopment, and are able to run about and 

 eat as soon as they are born. 



In the Marsupialia the pelvis is also much 

 developed, both to afford attachment to the 

 powerful muscles of the tail and hinder legs, 

 and, in some of the order, to support the ab- 

 dominal viscera in their sitting posture and 

 leaping movements. It is remarkable for the 

 development, in most of the genera, of two 

 extra bones (fig. 99. a.) characteristic of the 

 order, which are attached to the pubes in the 

 site of the crests and spines of these bones in 

 other animals, and support the abdominal 

 pouch peculiar to them and destined for the 

 reception and more mature development of 

 their young, expelled immature from the pelvic 

 cavity. They are directed obliquely forwards 

 and a little outwards, in the direction of the 

 fibres of theaponeurosisof the external oblique 

 muscle of the abdomen; in which, according 

 to Owen and Laurent, these bones are de- 

 veloped by ossification of the fibrous tissue. 

 The free extremities are a little curved, and 

 over them the cremaster muscles in the male 

 animals play. The pelves of the Marsupials 

 differ considerably, according as the mode of 

 progression is quadrupedal, or by a succession 

 of springs from the tail and strong hinder ex- 

 tremities. The Wombat may be taken as an 

 example of the former, and the Kangaroo of 



