THE SKELETON OF THE VERTEBRATE HEAD. 151 



the passage of the olfactory nerve through a notch or hole in 

 its upper edge. I regard this process on each side of the pre- 

 sphenoidal centrum as of the same nature as the process which 

 will be found projecting from each side of the lower part of 

 the ethmoidal septum or centrum, and which, abutting against 

 the descending process of the ethmoido-frontal, forms a wall 

 or rampart across the floor of the nasal passage, extending 

 nearly half-way up to its roof, immediately behind the ex- 

 ternal nostril, thus converting that part of the nasal chamber 

 in front of it into a vestibule. This process is largely de- 

 veloped in the ossified ethmoido-vomerine septum of the 

 hawks and owls. 



I would here observe that the " os en forme de cuiller " of 

 Cuvier, which he considers as the inferior turbinal of the 

 lizard, and which forms the fore part of the floor of the nostril 

 on each side, and the convex anterior part of which stretches 

 like a buttress across the cavity, between the septum and the 

 maxillary, immediately behind the external nostril, appears 

 to me to be, with its fellow of the opposite side, merely the 

 ossified lower portion of the ethmoidal centrum. These so- 

 called " cornets inferieurs " of the lizard form the floor, and 

 do not, therefore, project from the outer wall of the nasal 

 passage in the manner of the inferior turbinals ; and I believe 

 anatomists will, in reviewing the subject, admit that the in- 

 ferior turbinal accompanies the fully-completed maxillary 

 arch, and only exists, therefore, in the mammal. 



I regard these lateral processes of the ethmoidal and pre- 

 sphenoidal centrums of the bird as homologous with the 

 pterygoid processes of the post-sphenoidal centrum, and 

 generally with those processes which, under various forms, 

 project downwards from the sides of the lower or haemal 

 aspects of the occipital and succeeding centrums in certain 

 fish, or with those processes termed " hypopophyses" by 

 Professor Owen. 



