Maternal Organs of Reproduction in Animals. 257 



the force of a blow. The liquor amnii, with its investing mem- 

 brane, is also made to serve a no less important office, that of 

 being protruded into the mouth of the womb at the commence- 

 ment of parturition, thus acting as a hydrostatic dilator. 



The allantoid membrane is situated between the amnion and 

 corium, where it forms a sac to receive the urinary secretion of the 

 loetus : it is of large size in the lower animals, and its dimensions 

 increase with the growth of the foetus, a phenomenon which is not 

 observed in the human subject. The allantoid sac has a direct 

 communication with the true urinary bladder by means of the 

 urachus (see Plate, yj. The umbilical cord, h, is composed of 

 this tube, the urachus, and the arteries, i, which convey the im- 

 pure blood out of the body of the foetus to the cotyledons, and the 

 veins, J, which return it after having been re-oxygenated in the 

 manner previously alluded to. It will be evident from the fore- 

 going remarks, that a due provision is made for an equal distribu- 

 tion of this pure blood through the body of the foetus, so that every 

 part of the frame may be built up at the same time; consequently 

 we meet with vessels in the foetus that are not needed after birth. 

 To enter more fully into this interesting and instructive subject, 

 would be to encroach on the practical part of our lecture, and 

 therefore 1 proceed to speak of the symptoms of pregnancy and 

 the period of utero-gestation. 



Explanation of the Plate opposite. 



a. — The interior of the uterus, studded with, h, f. — The urachus, or passage through which the 



the maternal portions of the cotyledons. urine is conveyed to the allantoid sac. 



c, — The outer surface of the corium, with the g. — The amnion, the membrane which enve- 



tufts of the foetal vessels, some of which lopes the foetus, and secretes the fluid in 



are seen in union with the maternal which it floats. 



portions of the cotyledons. h. — The umbilical cord, showing, i, the arte- 



d. — The inner surface of the corium. ries conveying the impure blood to the 



c. — The allantoid membrane, which forms a cotyledons, and, ;, the veins returning 



receptacle for the urinary secretion of the it after its purification. 



foetus. 



The first and most striking indication of impregnation is the 

 cessation of oestrum, the animal not returning to the male at the 

 usual period, or refusing his overtures when introduced to him. 

 With this is associated a general quietude of the system and a 

 tendency to accumulate flesh, and in some animals, as the mare, 

 a sluggishness while at work. Shortly afterwards the abdomen is 

 found to increase in size, the loins to droop, and the muscles of 

 the croup to be less prominent. The labia pudendi are swollen and 

 flaccid, a blush of redness pervades these parts, extending into the 

 vagina, from which an augmented quantity of mucus is discharged. 

 The abdomen gradually gets larger and larger, and has a peculiar 

 round appearance at its lower portion, with a falling in immedi- 

 ately beneath the bones of the loins. As the period of labour ap- 

 proaches, the mammary gland enlarges, the secretion of colostrum 



VOLi X. s 



