120 ON THE MORPHOLOGICAL CONSTITUTION OF 



as the ascending processes of their intermaxillaries, which 

 occupy the proper position of the nasals, have not been ob- 

 served as separate centres of ossification ; and as the greater 

 number of chelonian reptiles want these bones, and resemble 

 birds in the general character and horny covering of their 

 beaks, I am inclined to believe that the nasal bones are defi- 

 cient as ossified elements in the bird. In young birds, aiter 

 boiling or maceration, the osseous elements of the beak may 

 be removed, and the anterior part of the primordial cranium 

 brought into view. In the fore part of its septum we again 

 recognise the vomerine centrum, but more or less deficient in 

 certain birds from the septal perforation peculiar to them. 

 The upper margin of the cartilaginous septum, where it is in 

 contact with the ascending processes of the intermaxillaries, 

 flattens out into a lamina, which partly roofs over the external 

 nostril on each side. These marginal processes of the cartila- 

 ginous vomerine centrum extend down in front, so as to line 

 the fore and under part of the nasal fossse, projecting some- 

 what behind the intermaxillary margin of the external nostril. 

 The broad projecting upper portion of the cartilaginous septum 

 occupies the position of the nasal bones, while the inferior 

 portions project from behind the interrnaxillaries, like oper- 

 cular actinapophyses. In the chick the part of the primor- 

 dial cranium just described as belonging to the vomerine 

 sclerotome presents an opaque aspect and fibro-cartilaginous 

 structure, contrasting with the hyaline cartilage posterior to 

 it a peculiarity pointed out by Eeichert as characteristic of 

 certain portions of the primordial cranium. It will be ob- 

 served that I do not consider the bone or bones usually called 

 " vomer" in the bird as correctly designated. In the sequel 

 I shall indicate the grounds on which I hold these bones to 

 be the upper elements of the palatine arch. 



The Vomerine Sclerotome in Chelonian Reptiles. The inter- 

 maxillaries in the chelonian, united below, complete the front 



