VIII.] THE COLUMELLA. 245 



'basi-hyal' (Fig. 79, hh.), and two rods, one on each 

 side, the ' cerato-hyals ' (Fig. 79, ch.). 



In the third arch, which corresponds with the first 

 branchial arch of the Ichthyopsida, there is on each 

 side a large distal cartilaginous rod (Fig. 79, cbr.), the 

 ' cerato-branchial,' and a smaller proximal piece (Fig. 

 79, ebr.); between the two arches lies an undefined 

 mass (Fig. 79, bbr), the ' basibranchial.' In the arches 

 behind this one there is in the bird no development of 

 cartilage. 



The lower part of the hyoid arch, including the 

 basi-hyal, unites with the remnants of the arch behiud 

 to form the hyoid bone of the adult. 



The fenestra ovalis and fenestra rotunda appear 

 on the seventh day as spaces in the side walls of the 

 periotic cartilage. The former is filled up by a small 

 piece of cartilage, the stapes (Fig. 78, st), which in the 

 adult forms part of the columella (see pp. 166, 167). 



The columella is believed by Huxley and Parker to represent 

 the independently developed dorsal element of the hyoid, together 

 with the stapes with which it has become united. 



For further details of the development of the skull 

 we must refer the student to Professor Parker's Memoir 

 upon the Development of the SkuH of the Common 

 Fowl (Gallus domesticus), Phil. Trans., 1866, Vol. CLVi., 

 pt. 1, and to the chapter on the Bird's skull ia the 

 Morphology of the Skidl, by Professor Parker and 

 Mr Bettany. 



We shall conclude this account by giving a table of 

 those bones which are preformed in cartilage, and of the 

 purely splint or membrane bones. 



