THE SKELETON OF THE VERTEBRATE HEAD. 143 



centrum of the pre-sphenoidal sclerotome, of which the orbito- 

 sphenoids are the neurapophyses. The proper "os en ceinture" 

 of Cuvier is in fact the homologous structure in the aneurous 

 batrachian with the so-called "ethmoid," and the orbito- 

 sphenoids collectively in the bird ; the centrum being prin- 

 cipally developed in the latter, the neurapophyseal elements 

 in the former. On these grounds, and also because I hold, 

 with Cuvier, the * nasals " of the frog to be its " pre-frontals," 

 I cannot assent to Professor Owen's doctrine that the " os en 

 ceinture " exhibits a stage in the mesial coalescence of a pair 

 of " pre-frontals," the final effect of which is the formation of 

 a mesial ethmoidal plate, or mesially-united nasal neura- 

 pophyses. 



On the Actinapophyses of the Ethmoidal Sclerotome. As 

 the radiating elements of the ethmoidal segment of the skull 

 are numerous and important, and as their elucidation requires 

 a more extended reference to corresponding elements in the 

 succeeding sclerotomes than can be made before the exami- 

 nation of these has been entered upon, I shall at present make 

 only a general statement on the subject. 



In the mammal we find a series of sclerous elements 

 arranged from above downwards on each side of the ethmoidal 

 sclerotome. On its upper or neural portion are the olfactory 

 " capsule " and the lachrymal bone. On the lower or haemal 

 portion, the cartilages of the eyelids, with the inferior turbi- 

 nated and malar bones. If the secondary antero-posterior 

 elongation of the maxillary be kept out of view ; and if it be 

 conceived in its fundamental developmentary form as a rib- 

 like bone, the convexity of which is inclined outwards and 

 backwards ; and if, at the same time, the possibility of a double 

 arrangement of actinapophyseal elements in each sclerotome 

 be borne in view, it will be seen that the malar extends out- 

 wards and backwards from the anterior or outer ; the inferior 

 turbinal from the posterior or inner aspect of the bone. I 



