130 ON THE MORPHOLOGICAL CONSTITUTION OF 



relations in the bird, but on the varied relations exhibited by 

 their corresponding parts in reptiles. 



The maxillaries or hsemapophyses of the ethmoidal sclero- 

 tome are feebly developed in the bird. Connected above, 

 chiefly to the descending processes of the ethmoido-frontals, 

 and more or less prolonged in the antero-posterior direction, 

 the maxillaries do not invariably complete the haemal arch. 

 Their region, therefore, of the palate, is more or less completely 

 occupied by the neurapophyseal plates of their own sclerotome. 



The Etlimoidal Sclerotome in the Chelonian. The connec- 

 tion of the maxillaries of the tortoises and turtles, by means 

 of the ascending processes of these bones, with the so-called 

 pre-frontals, appears to me to indicate that the latter are 

 homologous with the ethmoido-frontals of the bird, or the 

 frontals of Mammalia. I recognise in them the meta-neura- 

 pophyses of the ethmoidal sclerotome. Each of these bones 

 sends down from its posterior margin a lamina, concave in 

 front, and forming, with the concave under surface of the bone 

 itself, the posterior superior hollow of the nasal fossa. The 

 inner margins of these two descending laminae give attachment 

 to the anterior margins of the fibre-cartilaginous laminae, 

 which bound laterally the compressed pre-sphenoidal neural 

 space, and form the so-called interorbital septum. The inner 

 margins of the two descending frontal laminae are, therefore, 

 separated from one another above by the breadth of the fore 

 part of the groove on the mesial part of the under surface of 

 the combined so-called "frontals." If now the macerated 

 skull of the turtle be examined, it will be found that a 

 complex bony piece, the so-called "vomer," connects by its 

 pair of short divergent upper processes the inferior extremities 

 of the inner margins of the descending frontal processes, con- 

 verting the space between them into a triangular orifice. This 

 so-called vomer, after sending a horizontal plate backwards 

 between the palatines to form the mesial portion of the 



