714 DEVELOPMENT OF THE COMMON PHALANGER, 



does not yet completely divide the ventricles. The septum 

 intermedium, however, is distinctly more developed. The con- 

 dition of tlie main blood vessels is very similar : the right and 

 left umbilical veins, though now much closer together, still open 

 independently into the liver. 



Lungs. — The degree of bronchial ramification is now con- 

 siderably in advance of the condition in the seven weeks' human 

 foetus. 



Alimentary canal. -In this embryo the alimentary canal is 

 unfortunately damaged in the region of the umbilicus, but the 

 canal, so far as preserved, differs but little from that in Embryo 

 A. The lumen of the cesophagus, for a considerable distance, is 

 exceedingly small. The pancreas and liver are both fairly well 

 developed. 



Urinogenit<il system. — The mesonephros is considerably further 

 developed than in Embryo A, the tubes being more convoluted, and 

 the glomeruli very considerably larger. The epithelial process 

 representing the pelvis of the true kidney is now mai-kedly 

 lobulated, and well differentiated from the ureter. The genital 

 ridge is much more marked. 



Embryo D (10-5 mm. as preserved in picro-sulphuric acid). 



Plate XXII., fig, 4. 



Embryo E (11 mm.). 



These two embryos are in as nearly as may be the same stage 

 of development. The embryo figured was preserved in picro- 

 sulphui'ic acid, and measures 10'5 mm., but there is no doubt 

 that, as compared with the other embryos, it has been appreciably 

 more contracted, and that had it been preserved in a similar 

 medium, it would have measured at least 11 mm. Embryo E 

 was considerably damaged on one side, and unfortunately a com- 

 plete drawing of it was not made before it was cut ; but from 

 careful drawings of the head and limbs, the agreement with 

 Embryo D is so marked that it has not been considered necessary 

 at present to cut this latter, which will serve for the description 

 of the external characters ; the internal organisation of the same 



