906 



PARTURITION. 



which the fcetus attains a size utterly incom- 

 patible to pass through the small pelvis of the 

 mother were it not for the extraordinary elas- 

 ticity of the pubic ligament, being capable of 

 allowing the ends of the pubic bones to diverge 

 from each other to the distance of nearly an 

 inch and a half. The capability of the pelvis 

 being enlarged by this mechanism depends upon 

 the shortness of its transverse, and the great 

 length of its antero-posterior or sacro-pubal 

 diameter, the ossa innominata running forwards 

 from each side of the sacrum in a nearly parallel 

 direction, or rather forming an isoskeles triangle, 

 its apex at the pubes, its base at the sacrum. 

 This greater length of the antero-posterior to 

 that of the transverse diameter may be traced 

 with few exceptions along the whole chain of 

 pelviferous vertebrata until we reach the human 

 subject, and even here, until the age of puberty, 

 we find a similar relation between these dia- 

 meters. This form of pelvis is eminently 

 adapted for dilatation during parturition ; the 

 ossa innominata, moving, as it were, upon a 

 hinge at their sacro-iliac synchondroses, are 

 capable of a considerable separation at their 

 pubic ends, by which means the pelvis is 

 greatly enlarged and passage of the foetus much 

 facilitated. 



In some animals, as cows, the swelling and 

 softening of the ligamento-cartilaginous unions 

 is distinctly seen on the approach of labour, 

 the lumbar vertebras and sacrum sinking be- 

 tween the ilia, and these bones " slipping," as 

 it is called, over each other at their sacro-iliac 

 symphyses as the animal moves her hind legs. 



The axis of the pelvis in animals being with 

 few exceptions parallel with the spine, and the 

 outlet from the formation of the sacrum being 

 so large, it will be seen that up to the Rumi- 

 nantiathe mechanism of parturition is extremely 

 simple, the more so as until we reach this class 

 the uterus in great measure preserves its tubu- 

 lar formation, rendering it next to impossible 

 that the foetus should come in any other direc- 

 tion than with its long diameter corresponding 

 to the axis of the canal through which it has to 

 pass. 



In the Marsupiata the foetus is expelled at so 

 early a stage of developement, and is therefore 

 so small, that little or no dilatation of the pelvis 

 is required ; in these animals we see the pelvis 

 well developed, and the difference between the 

 length of the transverse and antero-posterior 

 diameters inconsiderable : in them it is probable 

 that little or no separation of the pubic bones 

 takes place during parturition. 



In the other and higher classes of the Mam- 

 malia the hard and well developed head of the 

 fcetus and its inflexible limbs, especially in the 

 Ruminantia,as also the horse, ass, &c., present 

 very considerable obstructions to its passage 

 through the pelvis, and require that it should 

 take a certain position during labour in order 

 that it may be born with such a degree of faci- 

 lity and within such a period of time as shall 

 not endanger its own life or that of its mother. 



Although the pelvis among the higher Mam- 

 malia still presents many remarkable points 

 of difference fiom that of the human race, least 



perhaps in the Quadrumana, still on the other 

 hand the mechanism of parturition in these 

 animals resembles in many respects this process 

 in man. The embryo has a somewhat similar 

 position in the uterus as it has in the human 

 subject. In the early periods of pregnancy in 

 both cases, the limbs stand off from the trunk, 

 whereas in the latter months they are pressed 

 close to the body. The lower extremities or 

 hind legs in animals are always turned upon 

 the abdomen ; in some instances the knees are 

 bent, in others not. 



The arms of the child are crossed upon the 

 breast; in animals the forelegs are usually 

 placed along the side of the head and generally 

 a little below it ; it is rare that one or both are 

 found above the head, although it has some- 

 times occurred that the two forelegs have been 

 found crossing each other over the head. The 

 forelegs are seldom found bent down under the 

 abdomen. 



The embryo usually lies upon its belly, or 

 on one side ; and from being scarcely ever 

 found upon the back it may be presumed that 

 this position is very rare.* The head is mostly 

 turned towards the os uteri, although cases are 

 by no means uncommon, even among the larger 

 animals, of its being turned to the fundus uteri. 

 In the larger animals (mare, cow, sheep, goat, 

 &c.) the embryo at first lies tolerably uncon- 

 strained, whereas at a later period it descends 

 into the smaller part of the uterus, and hence at 

 this time we usually find the nose bent down 

 upon the breast. In the child this position 

 with the chin upon the breast exists from a very 

 early period. 



In the smaller animals, viz. the dog, cat, rat, 

 &c., the head at the end of pregnancy mostly 

 lies flat on the lower jaw, and therefore presents 

 with the nose, whereas in the larger animals 

 the occiput presents, and this probably with- 

 draws again as labour comes on. The ears 

 are always pressed close to the head, being 

 turned either forwards or backwards; they are 

 usually found bent forwards in the dog, cat, 

 and horse, and backwards in the cow, sheep, 

 goat, rabbit, hare, &c. 



Although the human foetus usually presents 

 also with the head, the whole mechanism of its 

 parturition is very different from that of the ani- 

 mals above-mentioned ; the angles of the pelvic 

 axes with the spine and with each other, and 

 the relative size of the antero-posterior and 

 transverse diameters, are so different that we 

 find the greater part of the process subservient 

 to laws which do not exist in the lower animals; 

 nevertheless the grand primary law with which 

 we commenced holds equally good in the hu- 

 man subject as in the lowest ovipara, and upon 

 this depends the great distinction between 

 natural and unnatural presentations; for so long 

 as the long diameter of the child is parallel 

 with the axis of the passage through which it 

 comes, the child will present with its cephalic 

 or its pelvic extremity, and can be born in that 

 position; whereas if its long diameter does not 

 correspond with that of the axis of the pelvis, 



* Joerg. 



