1867.] 253 [Wj-man. 



would antacionize each other in their action ; the fore limbs, if ex- 

 tended, would, in consequence of their obliquity, tend to push the 

 body upwards and backwards, and the hind limbs under the same 

 conditions upwards and forwards. The two acting together would 

 give rise to a resultant motion upwards. By the rotation of the fore 

 arm in the embryo the action of the fore limb is reversed, and thus in 

 the forward movement of the body cooperates with, instead of antag- 

 onizing, the hind limb. 



When fully developed, therefore, the fore and hind limbs of ani- 

 mals have a general symmetry except in the following respects ; the 

 bones of the fore arm cross each other, while those of the legs do not, 

 and the toes and fingers are both directed forwards, li', however, the 

 fore arm be rotated outwards through half a circle, so as to make 

 the bones parallel, as in the leg, thus counteracting the change which 

 took place during development, the general symmetry would be 

 restored, and be complete. There would, however, exist a certain 

 amount of special asymmetry in the position of the thumb and great 

 toe, for these would be on opposite sides of the two limbs. Of this 

 difficulty we shall speak again further on. 



The symmetry of disease to which attention has of late years been 

 called,* also helps to sustain the idea of fore and hind symmetry. Cer- 

 tain maladies, as psoriasis, lej^rosy, syphilis, etc, not only attack cor- 

 responding or symmetrical portions of right and left parts, but also of 

 fore and hind parts. Certain skin diseases attack the backs of the 

 hands and feet, or the palms and soles, or the elboAvs and knees. The 

 earthy deposits in the arteries show a similar tendency to symmetrical 

 distribution. Such instances, however, are quite rare in comparison 

 with the vast proportion of diseases in which no such tendency is ap- 

 parent. They nevertheless tend to show that homologous parts, either 

 on the right and left, or fore and hind parts of the body, have such a 

 constitution that they are more amenable to the influence of a given 

 disease than other parts. 



We pass by only with a mention a third kind of symmetry, which 

 has been much insisted on by some anatomists, viz., that between the 

 dorsal and abdominal parts. Under certain circumstances this kind 

 of symmetry becomes almost exact, as may be seen, for exam])le, in a 

 vertical section of the tail of a fish, where the arrangement of the 

 bones, etc., below a horizontal line, passing through the vertebral col- 

 umn, is only a reversed copy of the jjarts above. 



, * Williafli Budd. Medico-Cliirurgical Transactions, London. Vol. xxv, 1852. 



Janic.-i I'ajret. Surgical I'athulogy. riiiladelpliia. 1860. p. 27. 



Uurt G. Wildor. I'atliologi'cal I'olaritics or Wliat lias beou called Symmetry 

 in Uisease. liuston Medical and Surgical Journal, April 5tli, 18GG. 



