THE SKELETON OF THE VERTEBEATE HEAD. 149 



adduced with regard to the ethmoido-frontals, and to the 

 statements to be afterwards made in regard to the meta- 

 neurapophyses of the post-sphenoidal and temporal sclero- 

 tomes. In the meantime, I shall confine myself to a general 

 exposition of the arrangement as I regard it. 



The anterior part of the body of the human sphenoid, and 

 the corresponding pre-sphenoidal piece in the Mammalia gene- 

 rally, constitute an undoubted centrum, to which the lesser, 

 anterior, or orbito-sphenoidal wings, are the corresponding 

 neurapophyses. 



How far we may be entitled to assume the frequent 

 " triquetral " bones in the coronal suture in the human, and 

 in certain other mammalian crania, and the separately-de- 

 veloped antlers of the giraffe, as indications of the missing 

 bone, remains to be determined. I would only observe at 

 present, that the great extent and permanency of the anterior 

 fontanelle appear to be connected with the deficiency in 

 question. 



I have already stated that I regard the so-called " principal 

 frontal " of the bird as the missing frontal of the mammal. 

 Distinguishing it as sphenoido-frontal, it is the divided meta- 

 neurapophysis corresponding to the feebly-developed " orbito- 

 sphenoids," which, bounding the optic and olfactory orifices, 

 constitute the neurapophyses, and to the so-called " ethmoid " 

 as the centrum of the pre-sphenoidal sclerotome. Assuming 

 for the present the signification I have attached to the " prin- 

 cipal frontals," and holding the neurapophyseal character of 

 the orbito-sphenoids as incontestable, I would only add a few 

 remarks regarding the central element. The determination of 

 the "ethmoid" of the birds as the centrum of the pre-sphenoidal 

 segment of the cranium, while it does not require Professor 

 Owen's hypothesis of connation of this element with the cen- 

 trum behind, presents the element under a form similar to 

 that exhibited by the ethmoidal and vomerine centrums. It 



