K. E. VON BAER. PHILOSOPHICAL FRAGMENTS. 20? 



Mammals passes to the left in order to reach the stomach, this 

 opposed direction is only produced by the influence of the sto- 

 mach, which, in order to propel to the right, lies towards the 

 left. It is also only the posterior part of the oesophagus which 

 is overruled by the stomach ; for when the bony skeleton of the 

 neck is so much bent that the oesophagus passes away from its 

 under surface, the oesophagus always, if 1 err not, lies on its 

 right side with the exception of its posterior extremity. I found 

 its position thus in Birds, in Chelonia, in the Camel, in the 

 Sloth, and probably in many other Mammals the same holds 

 good. When in Birds a special crop is developed, this also is 

 placed upon the right side. The course of the motion from the 

 pharynx, therefore, which is produced by the powerful constrict- 

 ors, is in general towards the right side. Compare arrow 6*. 



The course of the bile generally is from the right to the left ; 

 but this reversed direction may be regarded as dependent upon 

 the position of the liver, which is thrust to the right side in con- 

 sequence of the predominant current of the portal blood. In fact, 

 in the course of embryonic development, the liver passes to the 

 right side in proportion to the separation of the portal system 

 from the other vessels. 



As respects the sexual organs, they are as a rule tolerably 

 symmetrical, in consequence of their intimate connexion with 

 the animal body, which is rendered evident not only by their 

 position in the adult, but especially by the history of develop- 

 ment. Where, however, symmetry is less prominent, as for 

 example in the hen-bird only, the left oviduct is developed, and 

 the egg therefore is moved from the left towards the right side. 

 The direction of this movement is exhibited by the arrow 8. 

 Hitherto all the arrows which have been drawn have their points 

 directed towards the right side. The urinary passages only ap- 

 pear not to harmonize with this law. When the kidneys upon 

 the two sides do not agree, as in the Ophidia, it is that of the 

 right side, which is longer and placed more anteriorly. The 



* That the passage from right to left again is submitted to a determinate 

 standard, that therefore a definite form of spiral canals might be demonstrated 

 when the current cannot be continued to the right side, scarcely admits of 

 doubt. Yet here the perturbations are so frequent, and the discovery of the 

 type is so difficult, that this attempt would carry us too far. Besides, I con- 

 sider the current to the right to be that which is predominant and common to 

 all systems, and for our present purpose it is sufficient. 



