118 ON THE MORPHOLOGICAL CONSTITUTION OF 



mammalian series is uot only dependent on the nasal fossae, 

 but on the intermaxillaries, with which, as will be shown in 

 the sequel, it is invariably connected. Its passage backwards 

 under the centrum of the ethmoidal sclerotome to abut against 

 that of the pre-sphenoidal, is, as will also appear, a mamma- 

 lian peculiarity, and an instance of that antero-posterior elon- 

 gation and of that overlapping arrangement so frequent in the 

 adaptation of the cephalic centrums to one another. 



When the inferior turbiiial bone, an actinapophysis of the 

 ethmoidal sclerotome, is highly developed, as in the ruminants, 

 a strong flattened bar of fibro-cartilage is attached to the 

 inner aspect of the ascending process of the intermaxillary, 

 and widening out into a soft curved cartilaginous plate, com- 

 pletes the fore part of the inferior turbinal, connecting it at 

 the same time to the second actinapophysis or turbinal pro- 

 cess of the ali-nasal cartilage. I look upon this appendage as 

 a hsemactinapophysis of the vomerine sclerotome ; and serially 

 homologous with the second or turbinal hsemactinapophysis of 

 the rhinal, and with the turbinal haemactinapophysis of the 

 ethmoidal sclerotomes. These hsemactinapophyses have all 

 of them been enclosed within the nasal chamber during de- 

 velopment ; having passed in through the metasclerotomic 

 clefts, instead of forming parts of the nasal w^all, or projecting 

 from its outer aspect. 



Vomerine Sclerotome in the Crocodiles. — It is remarkable 

 that the familiar fact of the peculiar position of the external 

 nostrils of the crocodiles should not hitherto have attracted 

 attention. They open in front of the intermaxillaries as in 

 the mammals ; whereas, in the typical lacertians, and in the 

 extinct plesiosaurs, ichthyosaurs, and pterodactyles, in the 

 ophidians, amphibians, and birds, they open behind these 

 bones. On this peculiarity in the crocodiles depends the very 

 perfect development of the anterior part of the nasal septum. 

 Along with the complete and pervious intermaxillary arch, we 



