128 ON THE MORPHOLOGICAL CONSTITUTION OF 



halves of a metaneurapophysis. They are more or less 

 elongated in the antero-posterior direction ; and they bound 

 the posterior margins of the external nostrils by the descend- 

 ing processes which connect them with their maxillaries. To 

 distinguish them from the metaneurapopjiyses of the pre- 

 sphenoidal sclerotome, I designate them ethmoido-frontals. 



The arrangement of the centrum and neurapophyses of 

 this sclerotome in the bird appears to me to have been in a 

 great measure overlooked, from having been examined in the 

 macerated skull, in which these parts, as consisting principally 

 of cartilage, are to a great extent absent. 



The centrum consists of the posterior and greater part of 

 the mesial cartilaginous lamina, the interior portion of which 

 forms the vomerine centrum. The ethmoidal portion of this 

 laminar mesial cartilage flattens out at its upper margin, in 

 the same manner as the vomerine portion in front ; and like 

 the flattened upper edge of the so-called " ethmoid bone "- 

 the centrum of the presphenoidal sclerotome behind. In the 

 same manner as the flattened upper margin of the vomerine 

 portion extends outwards on each side, so as to form a hood 

 over the upper and fore part of the external nostrils, the 

 flattened upper margin of the ethmoidal portion of the septum 

 passes outwards on each side, under cover of the ascending 

 processes of the intermaxillary, and under the ethmoido- 

 frontal, extending down more or less to the level of the 

 palatal plate of the maxillary, and then turning in towards 

 the mesial plane, approaches or meets the lower margin of the 

 mesial lamina itself. Posteriorly, these curved cartilaginous 

 plates close in upon the posterior margin of the septum ; 

 which is not continuous with the anterior margin of the 

 laminar septum of the presphenoid. They are each, however, 

 perforated or notched for the transmission of the olfactory 

 nerve ; and they also leave on each side of the septum at 

 their posterior inferior angles, a space for the posterior nasal 



