918 



CLASS PISCES. 



round the cartilaginous palatopterygoid bar, there occur in Teleostei 

 the meso- and metapterygoid (fig. 843, Ms, Mtp). In the same class 

 the orbital region likewise develops a series of membrane-bones 

 round the eye, forming the suborbitals or orbital ring (ibid., 0, 0), 

 while the gill-cover or operculum (of which the first trace is found in 

 the Chimseroids in a fold from the hyomandibular overlapping the 

 first gill-slit) is formed by the preopercular, opercular, subopercular, 

 and infraopercular {ibid., Pr, Op, Sop, lop), which are broad, scale- 

 like membrane bones. In the branchiostegal membrane, which 

 unites with the gill-cover in closing the branchial chamber, there 

 is developed a number of branchiostegal rays (fig. 843, BsS, and 

 fig. 844, bo) ; but these may be partly or entirely replaced by 



Fig. 844. — Right side of the cranium proper of a Perch, together with the hyoid and bran- 

 chial arches, and the pelvic girdle, sh, Stylohyal ; eh, Epihyal ; ch, Ceratohyal ; bh, Basihyal ; 

 gh, Glossohyal ; tih, Urohyal ; bo, Branchiostegal rays ; cb, Ceratobranchial ; eb, Epibranchial ; 

 gr, One of the "gill-rakers" of the first branchial arch; pa, Parasphenoid ; so, Supraoccipital ; 

 pt, Posttemporal ; scl, Supraclavicular ; cl, Clavicular ; pel, The two pieces of the postclavicu- 

 lar ; sc, Scapula ; co, Coracoid. 



jugular plates, occupying the space between the rami of the man- 

 dible. The hyoid arch (fig. 844) is attached to the inner side of 

 the hyomandibular by a stylohyal {ibid., sh), articulating inferiorly 

 with the epihyal (eh), and the latter with the large ceratohyal (ch) ; 

 the two latter carrying the branchiostegals. The inferior part of 

 this arch is formed by the basihyal (bh), from which the glossohyal 

 (gh) extends forwards into the tongue, and posteriorly articulates 

 with the first of the basibranchials, mentioned below. The urohyal 



