370 MANUAL OF ZOOLOGY SECT. 



Immediately behind the lower jaw is the hyoid arch. 

 This consists of two cartilages on each side, and a 

 mesial one below. The uppermost cartilages is the hyomnn- 

 dibular (hy. ;;/.) : this articulates by its proximal end with a 

 distinct articular facet on the auditory region of the skull ; 

 distally it is connected by ligamentous fibres with the outer 

 ends of the palato-quadrate and Meckel's cartilage. The 

 lower lateral cartilage is the cerato-hyal (hy. en.}. Both the 

 hyo-mandibular and cerato-hyal bear a number of slender 

 cartilaginous rods the branchial rays of the hyoid arch (br. r.). 

 The mesial element, or basi-hyal, lies in the floor of the 

 pharynx. Behind the hyoid arch follow the branchial arches^ 

 which are five in number. Eich branchial arch consists of 

 several cartilages and bears branchial rays. 



The skeleton of all the fins paired and unpaired pre- 

 sents a considerable degree of uniformity. The main part of 

 the expanse of the fin is supported by a series of flattened 

 segmented rods, the cartilaginous pterygiophores or fin-rays, 

 which lie in close apposition : in the case of the dorsal 

 fins these are calcified along their axes. At their outer 

 ends are one or more rows of polygonal plates of cartilage. 

 On each side of the rays and polygonal cartilages are a 

 number of slender horny fibres of dermal origin. In the 

 smaller median fins there may be an elongated rod of cartil- 

 age constituting the skeleton, or cartilage may be entirely 

 absent. In the pectoral fin (Fig. 210) the fin-rays are 

 supported on three basal cartilages articulating with the 

 pectoral arch. The latter is a strong hoop of cartilage incom- 

 plete dorsally, situated immediately behind the last of the 

 branchial arches. It consists of a dorsal, or scapular (pct.g.) 

 and a ventral, or coracoid portion (pet. g .\ the coracoid portions 

 of opposite sides being completely continuous across the 

 middle line, while the scapular are separated by a wide 



