138 Mr. Flower Reply to Professor Owen. [Mar. 30, 



hemispheres are only partially connected by the fornix and the anterior 

 commissure ; in the rest of the class the corpus callosum is added." 



I will only cite one other instance to show that I am far from being sin- 

 gular in the outline I have given of the most important part of Professor 

 Owen's researches upon this subject. 



In the year 1851 the Copley Medal of this Society was awarded to Pro- 

 fessor Owen. In the epitomized account of his labours, the observations 

 upon the structure of the Marsupial Brain are referred to in the following 

 terms. I quote from the President's Address (Proceedings of the Royal 

 Society, Dec. 1st, 1851): "In the Philosophical Transactions for 1837 

 appeared a memoir from Professor Owen's pen, describing certain peculia- 

 rities in the brain of the Marsupialia, especially the absence of the corpus 

 callosum. The same condition he subsequently discovered in the Orni- 

 thorhynchus and Echidna. This, and other peculiarities of structure in the 

 sanguiferous, osseous, and dental systems, led Professor Owen to suggest 

 a modification of the classification of the mammalia which Cuvier had 

 adopted in his last edition of the ' Regne Animal.' Deeming modifications 

 of brain of more importance than those of ungual phalanges, and connect- 

 ing the higher development of the commissural system of the brain with 

 the longer sojourn of the foetus in the womb, and its more intimate union 

 therewith, Professor Owen, in his paper ' On the Classification of the 

 Marsupials' in the Trans. Zool. Soc. 1839, groups together all the 

 mammalia which have a placenta under any form, and which have a 

 corpus callosum, in a primary subclass, under the name of Placentalia ; the 

 rest form the Subclass Implacentalia, and this includes the orders Marsu- 

 pialia and Monotremata." 



This outline of the most important results of a series of anatomical re- 

 searches could not have been intended as a " zoological definition." If I 

 have misrepresented Professor Owen in stating broadly that he alleged 

 that the implacental mammalia were distinguished from the remainder of 

 the class by the absence of the corpus callosum, so also did the compiler 

 of the above paragraph ; and at least one of the reasons assigned for the 

 award of the highest honour the Society can bestow is grounded on a 

 misconception. The main difference as to questions of fact between Pro- 

 fessor Owen and myself may be stated briefly as follows. He has seen 

 and described, in the brains of the implacental mammals, a transverse 

 commissure between the hemispheres of the cerebrum, which he calls 

 ' fornix,' ' commissure of the hippocampi,' or sometimes ' rudimental 

 commencement of the corpus callosum.' This commissure he appears to 

 have seen (or at all events to have described) only in a portion of its extent. 

 lie has found in placental mammals a great transverse commissure super- 

 added to this, to which he generally restricts the term 'corpus callosum.' 



I have seen and described in the brain of several implacental mam- 

 mals the same transverse commissure, but have traced out its relations 

 and connexions more fully, especially by means of transverse and Ion- 



