207 



several vertebrate classes, directing attention to the tripartite divi- 

 sion of their distal segments, and to the uniformity of plan upon 

 which they are constructed. He argued that this uniformity has 

 relation to the mode in which their development proceeds, and to 

 the similarity of their functions rather than any adhesion to an 

 " ideal archtypal pattern ;" and expressed his belief that the exist- 

 ence of such an ideal in the minds of anatomists proves in some 

 measure a hindrance to the full study of the laws which regulate the 

 formation of animal bodies. 



The differences between the fore and hind limbs were shown to 

 depend,— first, upon the fact that the hind limbs are required to pro- 

 pel as well as to support the trunk, and less variety of movement is 

 needed in them ; hence they are larger and firmer, and the same 

 bone of the leg forms a main constituent both of the ankle and of the 

 knee-joint ; secondly, in walking and running the fore limb is ex- 

 tended in front of the trunk, and draws the latter after it during its 

 flexion, whereas the hind limb is bent up beneath the trunk and 

 drives the latter on before it during its extension. This antagonism 

 in the mode of their action leads to an antagonism in construction 

 of the two limbs, — of their upper segments at least, the posterior 

 aspect of the one corresponding with the anterior aspect of the other. 

 The antagonistic relations are brought about by a partial rotation in 

 the long axis of the two limbs which takes place in opposite directions 

 during development ; and coincident with the rotation of the proxi- 

 mal segments of the fore limb in one direction is a rotation of its 

 distal segment in an opposite direction, so as to turn the palm towards 

 the ground. 



Reasons were given for regarding the scapular and pelvic arches 

 as formed by modifications of the haemal, and not of the pleural, 

 parts of the vertebrae ; and for believing that the scapular arch be- 

 longs, not to the occipital bone, but to the vertebrae of the fore part 

 of the chest or of the hinder part of the neck. 



February 28, 1859. 



Dr. Donaldson read a paper " On Plato's Cosmical System as 

 exhibited in the tenth book of ' The Republic' " 



The author first gave a translation of the whole passage (Plato, 

 Resp. x. 616 B, 617 E), accompanied by a critical and philological 

 examination of the Greek text. He then undertook to show the 

 connexion between the fanciful picture of the universe which Plato 

 has here given, with his other speculations on the origin of things, 

 and especially with the occult philosophy of numbers. And he 

 argued, finally, that the tradition preserved by Clement of Alexandria, 

 which identifies Er, the son of Armenius, with Zoroaster, rests upon 

 a foundation in fact ; and that while there is good reason to believe 

 that the doctrines of Heracleitus and Zoroaster agreed in many essen- 

 tial particulars, and that Plato was well acquainted with the specu- 

 lations of the Ephesian philosopher, there are certain particulars in 



