THE ABDOJIEN. 255 



tends from tlie amnion to tlie chorion. The amnion 

 presents the characters of all other serous membranes, but 

 it contains the urine of tke foetus, since the allantoid sac 

 is brought into communication with the bladder of the 

 foetus (from which it was originally derived) by the 

 urachus, a tube running through the amniotic part of the 

 umbilical cord. The foetus in utero, therefore, is surrounded 

 by his own urine. The umbilical cord, therefore, is 

 divided into two parts : The allantoid portio7i consists simply 

 of two umbilical veins, and an umbilical artery surrounded 

 by the allantois. The amniotic portion, in addition, contains 

 the urachus, and those vessels which belong to the amnion. 

 In both parts the vessels receive coatings of embryonic cells^ 

 and in the amniotic portion the vessels are arranged spirally, 

 giving this part a rope-like appearance. Finally, we 

 may notice that the bladder of the foetus is larger in propor- 

 tion than that of the adult, extending to the umbilicus, where 

 it terminates in the urachus. That the so-called vascular 

 glands are largest in the foetus (in proportion) ; that the 

 kidneys are lobulated; the testes in the lumbar region in the 

 colt ; and the lungs, dark red solid organs, for they have 

 not yet been filled with air. When the labour-pains of 

 the dam occur the chorion is ruptured, and the amnion 

 with its serous layer is the first to protrude through the 

 external opening, being vulgarly termed the " water bag J' 

 On rupture of this the foetus is expelled, and sometimes in 

 falling ruptures the umbilical cord. The membranes 

 follow at variable periods. On first feeling the chill ex- 

 ternal air the young animal gasps, and so draws air 

 through the trachea, it permeates the air-vessels, and for 

 the rest of his life the animal is an air-breather. Those 

 communications between the several portions of the vascular 

 arrangement of the foetus, which are not required after 

 birth speedily become impervious ; if they are persistent 

 they cause disease. 



We may examine the attachments of some muscles 

 underneath the loins. 



Psoas magnus arises as far forward as the inner surface 

 of the last two ribs; it is attached to the transverse 

 processes of the lumbar vertebrae, and its fibres interiorly 

 join with iliacus in becoming inserted into trochanter minor 

 internus. Arteria profunda femoris runs across the in- 

 ferior tendon. 



