96 OBSTETRICAL PHYSIOLOGY. 



not complete, and hernia of the intestines exists at birth, or even for 

 some time after that event. 



With regard to the curious torsion of the cord on itself — as many as 

 twelve complete turns having been counted in the cord of a six-months- 

 old foetus — it has been held by some authorities that this is only acci- 

 dental, and depends on the movements of the foetus during the latter 

 stages of gestation, or the displacement it undergoes on leaving the 

 uterus ; consequently, that the spiral twisting of the vessels is not 

 normal. It is improbable, however, that the twisting can be due to 

 muscular movements of the foetus ; as it is unlikely these should be 

 entirely, or even mostly, in one direction. It has been recently 

 attributed to the excessive growth of the umbilical arteries, whereby 

 they are compelled to take a tortuous course ; and when a slight 

 obliquity has once been established, every pulsation will tend to increase 

 the spiral ; at the same time every movement of the foetus or the 

 mother would be taken advantage of, the cord and foetus revolving 

 together until, with the growth of the latter, the friction of the amnion 

 puts an end to the rotation. It does not appear that any advantage 

 accrues to either foetus or mother from the torsion of the cord ; on the 

 contrary, it increases the resistance to the flow of blood, and also 

 augments rather than diminishes the danger of stoppage of the circula- 

 tion by accidental pressure. Examination of non-displaced foetuses 

 proves that it is far from being constant. 



At birth, the umbilical cord is usually torn or gnawed through at a 

 short distance from the umbilicus of the foitus ; the remaining portion 

 dries up, dies, and falls off in a few days. 



SECTION III.— DEVELOPMENT OF THE ECETUS. 



Having studied the conception and partial development of the young 

 creature, and described the envelopes which surround it, we will pro- 

 ceed to notice the various changes which occur in it until gestation is 

 completed and parturition is about to take place. 



This division of our subject is of much importance in several respects, 

 but more especially with regard to the relation it bears to teratology — 

 the branch of science which treats of congenital defects, malformations, 

 and monstrosities. 



The transition from the condition of the embryo, when the young 

 animal has scarcely assumed a definite form, to that of the foetus, when 

 it presents the lineaments of the species to which it belongs, is very 

 gradual. 



The dorsal cord, as has been stated, is a cylindrical body developed 

 above the primitive furrow, with slightly attenuated extremities, and at ' 

 each side small opaque quadrangular masses, the vertebral lanmice, which 

 are in xQ^Miy the j^roto-vertebra , or first rudiments of thevertebrge. Each of 

 these masses is perforated by a small opening, and is resolved into three 

 portions — the proto-vertebral cavity, the muscular lamina, situated above 

 the cavity, and the proto-vertebra placed below the cavity. The muscular 

 lamincB, increasing in volume, are inflected upwards and at last unite on 

 the median line of the back, chiefly forming the muscles of the verte- 

 bral furrows ; they also send off prolongations downwards, which concur 

 in the development of the intercostal and abdominal muscles, as well as 

 those of the limbs. The proto-vertebrce, bend upwards and downwards 

 on each side, so as to enclose the proto-vertebral cavity or spinal canal. 



