PARTURITION. | 
tube and uterus, and where the fetus is gene- 
rally so large, the parturient process is equally 
simple, the uterus and vagina being converted 
by gradual dilatation into a simple continuous 
canal. In the higher classes of Reptilia we 
first perceive a regularly formed pelvis, viz. in 
the Sauria, and still more completely in the 
Chelonia, the pelvis in the latter being consi- 
derably advanced in point of developement, 
even as compared with the higher Mammalia ; 
indeed as regards pelvic developement these two 
classes of the Reptilia ought rather to be placed 
above the Aves, in whom, with one exception, 
the pelvis is much more imperfect. The rudi- 
mental trace of a pelvis which is seen in cer- 
tain of the fishes is evidently a modification of 
a scapula, and intended as part of the appa- 
ratus for propulsion, being connected with the 
ventral fin. In the Cetacea this is marked by 
the existence of two small thin flat bones im- 
bedded in muscle on each side the vent. In 
Birds this formation is still more marked, and 
here we first see distinctly the analogy pointed 
out by Meckel between the attachments to the 
trunk of the upper and lower extremities, the 
ilium corresponding to the scapula, the ischium 
to the coracoid process, and the pubic bone 
to the clavicle; the pelvis in them  pre- 
sents the transition from the scapulary bones 
_ of the lower extremities, if we may so call 
them, in some of the fish tribe, to the 
completely formed bony canal of the higher 
Mammalia. The pelvic bones in Birds are 
still subservient to little else than the purposes 
of locomotion, the ossa pubis not uniting in 
front, their points terminating at a considerable 
distance from each other, but connected bya 
ligamentous band which is elastic and capable 
of considerable dilatation ; the process of par- 
turition here is as simple as in the inferior 
classes, the egg passing along the cloaca through 
the half bony, half fibrous canal of the pelvis. 
One solitary instance of a perfect pelvis pre- 
sents itself among the Aves, viz. in the ostrich, 
and where the symphysis pubis does not seem 
capable of much dilatation, although from the 
size of the egg there can be but little room to 
Spare in the pelvis during its expulsion; an 
apparent approach to this formation is occa- 
sionally seen in birds which attain a consider- 
able age from the deposition of bony matter 
into the pubic ligament. An equally solitary 
example of an imperfect pelvis among the 
Mammalia is furnished by the lesser ant-eater, 
the pubic bones not being united. 
The lowest grade of parturition which (ex- 
cepting the Cetacea) is observed in the Mam- 
malia, is seen in certain Insectivora, viz. the 
mole, shrew, &c. in which this process is akin 
to that in those animals which either have no 
= at all, or have them of a very imperfect 
ind. In the mole, &c. the pelvie cavity is 
so small as to be utterly useless for the pur- 
poses of parturition, not even containing the 
rectum, which, together with the vagina, 
passes down in front of the pelvis. In this 
instance, therefore, we have once more a strong 
analogy to parturition in the lower ovipara, es- 
_ pecially as in the above-mentioned animals the 
| 
905 
uterus is still at a low grade of formation, being 
cylindrical and scarcely to be distinguished 
from its Fallopian tube. 
A still further advance towards the perfect 
pelvis is seen in the Guinea-pig, an animal in 
Fig. 487. 
Pelvis of the Guinea Pig at the time of parturition, 
Fig. 488. 
Pelvis of the Guinea Pig 72 hours after parturition. 
