238 THE DEVELOPMENT OF THE SKULL. [CHAP. IX. 



semicircular canal, for the epiotic, which is for a short time 

 distinct from the exoccipital. 



In chicks of about two months old, the sutures have begun 

 to lose their distinctness, but two new pairs of centres of 

 ossification appear adjacent to the presphenoid. These first 

 ossify independently, but afterwards set up ossification in the 

 presphenoid, which is still unossified. In fowls of from seven to 

 nine months, the splint bones are beginning to coalesce for the 

 most part with the other bones of the skull, and the sutures 

 are rapidly being obliterated. It would be beyond the scope 

 of this work to enter into the changes by which the skull of 

 the young chick, with most of the sutures distinct, developes 

 into the skull of the adult, where the lines of junction of 

 most of the bones are quite undistinguishable. We shall 

 therefore conclude by giving a table of those bones which 

 are preformed in cartilage, and of the purely splint or 

 membrane bones. 



Parts of the birds skull which are either preformed in 

 cartilage or remain cartilaginous. 



Supraoccipital. Exoccipital. Basioccipital. Epiotic. 

 Prootic. Opisthotic. Pterotic. Alisphenoid. Basisphenoid. 

 Orbitosphenoid. Presphenoid. Ethmoid. Post -frontal. 

 Septum nasi, turbinals, prenasal and nasal cartilages. Skele- 

 ton of the second and third visceral arches and stapes. 

 Meckel's cartilage and quadrate (first visceral arch). Ptery- 

 goid and palatine (superior maxillary process). 



Splint-bones not preformed in cartilage. 



Parietals. Squamosals. Frontals. Lacrymals. Nasals. 

 Premaxillae. Maxillae. Maxillo-palatiues. Vomer. Jugals. 

 Quadrato-jugals. Dentary and Bones of Mandible. Basi- 

 temporal and rostrum. 



