DEVELOPMENT OF THE ENDOSKELETON 



673 



ENTOGLOSS 



Fig. 318. Developmental stages of bird neurocranium. (A and B redrawn from De 

 Beer, '37, from De Beer and Barrington.) (A) Dorsal view of 8'/2-day stage of Anas 

 (duck). (B) Lateral view of 14-day stage of Anas. (C) Lateral view, adult stage of 

 Callus (chick). Cartilage = coarse stipple; bone = fine stipple. 



(fig. 315D). Each second visceral (hyoid) arch in the shark forms on each side 

 an upper hyomandibula, attached to the otic capsule by fibers of connective 

 tissue, a ceratohyal part, and a lower basihyal element (fig. 315D). 

 The basihyal portion of the two hyoid arches forms a basis for the so-called 

 tongue. The succeeding branchial arches form supports for the gills and de- 

 velop cartilaginous branchial rays which extend out into the gill area (fig. 

 315C). Each branchial arch on each side divides into four cartilages, namely, 

 the upper pharyngobranchial, and the lower hypobranchial, the epibranchial 

 and the ceratobranchial elements. The last two elements lie between the first 

 two, and the ceratobranchial element is articulated with the hypobranchial 

 element (fig. 315D). 



The visceral skeleton in ganoid and teleost fishes arises similarly to that 

 in elasmobranchs but becomes largely ossified in the adult (fig. 316). 



In the frog, the well-developed, visceral skeleton of the late larva becomes 

 greatly modified during metamorphosis and the acquisition of adulthood. The 

 hyoid arch persists in cartilage. The mandibular arch contributes to the forma- 

 tion of the upper and lower jaws. The lower jaw in the metamorphosed frog 

 consists of Meckel's cartilages, reinforced by membrane bones, the dentaries 

 and the angulospenials. The pterygoquadrate cartilages remain as cartilage 

 and are reinforced by the pterygoid, quadratojugal, squamosal, maxillae and 

 premaxillae, to form the upper jaw (fig. 317B, C and Table 1). 



In birds, the first visceral or mandibular arch contributes to the formation 

 of the quadrate and articulare at the angle of the jaw. These two bones on 



