80 LECTURE III. 



the different parts of the same plaster, or glue, casts may be 

 compared with each other, but not different gypsum, or glue, 

 casts, made at different times and with different materials. 

 The most unobjectionable substance in this respect would be a 

 metallic alloy which melts at the boiling-point of water. We 

 could then obtain, not merely the external form, but also the 

 weight, the specific gravity of the alloy having been deter- 

 mined. I do not, however, intend to take out a patent for the 

 discovery of a material for taking casts of the skull cavity; 

 for, if we go a little further into the matter, we find that it was 

 not an anatomist, but a physicist, who deserves the credit of 

 having first made use of such a substance. Lichtenberg, in 

 the famous auction catalogue of the curiosities of a deceased 

 gentleman, mentions a butter-dish in the form of a skull, 

 having the inner surface of the cover so modelled that it im- 

 pressed upon the butter the exact form of the brain ! 



The measurements of Welcker have shown that, in the 

 structure of the skull, a tendency generally prevails to estab- 

 lish, even when there is a considerable variation in total mass, 

 a nearly equal internal capacity. There also exists a certain 

 proportion between the size of the skull and that of the body, 

 although the proportion is not always the same for different 

 degrees of stature. Thus, though giants have generally a 

 larger skull than dwarfs, it is proportionally smaller in the 

 former than in the latter. Besides, the large skulls incline 

 rather to length, at the same time decreasing in width ; while 

 small skulls become more rounded, thus acquiring that form 

 which, for a given external surface, affords the largest internal 

 space. From long skulls of considerable size we may, there- 

 fore, generally infer that their possessors were tall, muscular 

 men, and it is known that among the Negroes, who are 

 characteristically long-headed, we frequently meet with strik- 

 ingly athletic forms. 



This will be the proper place to make some remarks on 

 sexual differences which occur within the same species and 

 variety, and which have hitherto not received the attention 

 they deserve. You are aware that, in the animal kingdom, 

 there are many instances in which this difference is so great, 



