PARTURITION. 



905 



lube and uterus, and where the foetus 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 Sauna, 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 by a 

 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 

 pelvis at all, or have them of a very imperfect 

 kind. In the mole, &c. the pelvic 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 



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 



Jig. 487. 



Pelvis of the Guinea Ply at the time of parturition. 

 Fig. 488. 



Pelvis of the Guinea Pifl7'~ hours after parturition. 



