MR. OWEN ON THE GENERATION OF THE MARSUPIAL ANIMALS. 363 



t, t. The two superior cavse. 



The pulmonary artery and aorta have the same relative position as in the 

 adult. 

 u. The rudiments of the posterior extremities. 

 V. The external orifice of the ear. 

 w. The branchial orifice. 

 Fig. 2. The viscera of the preceding foetus, more magnified : the heart is turned up, 



to show the auricles, and the whole intestinal canal is seen. 

 Fig. 3. Outline of the same foetus, natural size, showing the connexion of the um- 

 bilical vesicle. 

 Fig. 4. Outline of the embryo of the Goose, showing its natural size and state of 

 development when the allantois x, is just beginning to expand from 

 the lower part of the intestine. The brain may be observed to be pro- 

 portionately more developed than in the Kangaroo. 

 The same letters are used for the different parts as in fig. 1. 

 Fig. 5. Outline of the Kangaroo about twelve hours after uterine birth, showing its 

 natural size and external development at this period. The elongation of 

 the jaws has reduced the mouth to a simple round anterior orifice, which 

 subsequently becomes even more contracted before the lateral fissures 

 begin to extend backwards. The eye is concealed by the completely 

 formed eyelids. Three divisions are now seen at the posterior extremity. 

 A longitudinal line indicates the separation of the umbilical pedicle. 



a. The upper nipple of the left side, to which the above foetus was attached. 



b. The lower nipple of the same side. 



Fig. 6. Mammary foetus of the Pygmy Opossum (Petaurus pygmoeus), natural size. 

 6*. The same magnified and dissected, showing, 



a. The urinary bladder. 



b. The urachus. 



Fig. 7. Mammary foetus of the Kangaroo, about a fortnight old : natural size. The 

 parietes of the abdomen are removed, to show the increased development 

 of the viscera, as compared with the uterine foetus (fig. 1 .) ; and also the 

 urinary bladder a, and its attachment to the abdominal parietes. 



Fig. 8. Magnified view of the abdominal viscera of the same mammary foetus. 



a. The urinary bladder. 



b. The urachus. 



c, c. The umbilical or vesical arteries. 



d. The ligamentum suspensorium hepatis, in which there is no trace of umbi- 



lical vein. 



e. The left lobe of the liver. 

 /,/. The right lobe now subdivided. 



