216 KEPOET OF NATIONAL MUSEUM, 1887. 



It is not necessary here to consider the elements which compose or- 

 ganic form or the conditions that determine their arrangement. The 

 process, so far as the head is concerned, has been, to a great extent, 

 masked among the vertebrates by adaptation to other than encephalic 

 relations, while the part was carried through the cartilaginous, semi- 

 osseous, unamalgamated, and consolidated types of crania, to one which, 

 as representative of the most important organ in the body, has been 

 commonly selected by the anthropologists for investigation, aud generally 

 believed to promise results corresponding with its position and the 

 function it sustains. Tried by the tests afforded by craniometry, how- 

 ever, it appears to have little or no taxinomical value, since the outcome 

 of these measurements is to transpose races and fuse peoples otherwise 

 known to be distinct. 



At the same time, in man, cranial outlines are unquestionably pre- 

 ponderantly determined by the brain, while the features by which its 

 action is obscured have been so frequently and completely described that 

 they need not be recapitulated. But although this statement holds on 

 the morphological side of the question, from the physiological stand- 

 point the case is not the same. The brain limits the shape of the head 

 and is itself limited by the laws of growth, heredity, aud structural 

 tjorrelati vity ; but in the phenomenal series cerebral development is 

 antecedent to cranial evolution, and the relation subsisting between 

 these — a relation which is in its nature causal, so far as shape is con- 

 cerned — places the factors upon different planes. In virtue of prepon- 

 derant function and equivalent preponderance of structure in special 

 ganglia, a general form of head has been attained ; but from fluctuations 

 jn the energies by which it was produced in correspondence with varia- 

 tions in the conditions of life, this form varies both in human and pre- 

 human history, and so widely as to have thus far prevented classifi- 

 cation. 



That the organ through which all adjustments to the environment 

 are primarily made should vary among groups whose lowest aggregates 

 are nearly as passive to the direct action of natural selection as beasts, 

 and whose higher forms are but partially and incompletely adjusted, is 

 not surprising; and while it must be assumed upon biological grounds 

 that the plasticity of the brain has lessened since its deviation from the 

 ancestral type, whence issued in divergent lines that of man and his 

 congeners, still, the facts of descent suggest that to its organic variability, 

 and to that expressed in specific adaptations, there must be added a 

 strong inherited tendency in this direction. 



The cerebral history of the primates seems to warrant the theoretical 

 conclusion that among these great variability of the head exists. 



In Lemuridae, where the cranium relatively to the face is small, and 

 the ethmoidal, tentorial, and occipital planes are greatly inclined to- 

 wards the basi-cranial axis, the brain scarcely exceeds the base of the 

 skull in length, whereas in Simiadae the encephalon is more than twice as 



