SKELETON. 



155 



copulae become more or less intimately connected with each 

 other, thus forming a support for the whole visceral skeleton. 



The two anterior arches have somewhat different fates. 

 The second (counting from in front) is called the hyoid arch, 

 and it lies between the first true branchial cleft and the spiracu- 

 lar cleft (Eustachian tube, p. 73). In the fishes this arch is 

 divided into two primary pieces, a dorsal hyomandibular and a 

 ventral hyoid proper. The former loses more or less completely 



FIG. 164. Skull of cod, the outer membrane bones removed, after Hertwig. 

 A, angulare ; AR, articulare ; BR, branchiostegals ; DE, dentary ; EE, ectethmoid ; 

 EKT, ectopterygoid ; ENT, entopterygoid ; EPO, epiotic; PR, frontal; ff l ~^ t 

 hyoid; HM, hyomandibular; Iff, interhyal ; MA, maxillary; ME, mesethmoid; 

 MT, metapterygoid ; NA, nasal ; OCB, basioccipital ; OCL, exoccipital ; OCS, 

 supraoccipital ; P, parietal ; PA, palatine; PRO, prootic ; PS, parasphenoid ; PTO, 

 prootic; Q, quadrate; SPO, sphenotic; SV, symplectic. 



its connection with the hyoid, and intervenes between the jaws 

 and the cranium, where it forms the whole (elasmobranchs) or 

 a part (ganoids and teleosts) of a suspensor apparatus which 

 supports the jaws. In all forms higher than the teleosts this 

 hyomandibular element has apparently disappeared. 1 The hyoid 

 proper may divide into three parts, the epihyal, keratohyal, 

 and hypohyal, while a copula (basihyal), larger than the basi- 

 branchials, is usually developed, and not infrequently grows for- 

 ward to form an internal skeleton for the tongue. 



1 The stapes of the ear may possibly be derived from the hyomandibular. 



