MORPHOLOGY OF TELEOSTEAN HEAD SKELETON. 543 



the last to chondrify, it is the first to become completely 

 ossified. 



Similarly all the epibranchials {hr. e.) are ossified ; the 

 first is connected by its inner pointed extremity with the 

 anterior end of the second pharyngo-branchial; the second, 

 whilst still remaining fully connected with this, has also 

 taken on a still more intimate relation to the compound 

 pharyngo-branchial behind ; the third is slightly changed in 

 shape by the formation of a small cartilaginous process 

 dorsally, but otherwise, with the fourth, it retains all the 

 relationships of the earlier stage. Both pharyngo-branchials 

 (hr.p.) bear teeth and are completely ossified, though a little 

 cartilage remains at the anterior end. 



The basihyal {Jiy. h.) has become osseous for the greater 

 part of its length, its anterior portion alone being wholly 

 cartilaginous. The posterior portion sends down a keel 

 of bone, and abuts behind directly on the first basi- 

 branchial. 



Each hypohyal (fig. 13, ////. h.) has commenced to ossify 

 from two centres, a dorsal and a ventral. The outer surface 

 of the ventral forms a concave facet into which the convex 

 inner end of the ceratohyal {hy. c.) fits ; that of the other part, 

 on the contrary, is strongly convex, and fits into a corre- 

 sponding facet in the upper surface of the same bone. 



The ceratohyal occupies the whole of the rod-like, and the 

 lower third of the expanded portions of the original hyoid 

 cartilage. Externally the ossification extends into the 

 surrounding tissue, and thus partly encloses the upper 

 hypohyal; internally a similar but more laminar tistension 

 [liy. c.') overlaps a considerable part of the epihyal, which is 

 formed from the remainder of the cartilage. 



As in the previous stage, the hyomandibular (fig. 13, hym.) 

 exhibits the most striking change in shape. This time, how- 

 ever, the change is brought about by the rapid growth of the 

 anterior half of the lower border, whereby the stylohyal 

 [hy. i.) and the metapterygoid {'pg. m.) are carried a con- 

 siderable distance from the auditory capsule. Pollard (94, 



