372 MANUAL OF ZOOLOGY sect. 



lie in the sides and floor of the mouth-cavity or pharynx. 

 The first of these forms the upper and lower jaws. The 

 upper jaw, or palato-qitadrate (up. J), consists of two stout 

 rods of cartilage firmly bound together in the middle line 

 and bearing the upper (or anterior) series of teeth. The 

 lower jaw, or Meckel's cartilage (I. J), likewise consists of 

 two stout cartilaginous rods firmly united together in the 

 middle line, the union being termed the symphysis. At their 

 outer ends the upper and lower jaws articulate with one 

 another by a movable joint. In front the upper jaw is 

 connected by a ligament with the base of the skull. 



Immediately behind the lower jaw is the hyoid arch. This 

 consists of two cartilages on each side, and a mesial one in 

 the middle below. The uppermost cartilage is the hyo- man- 

 dibular (hy. m) ; 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 (liv. 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. Each branchial arch con- 

 sists 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 pterygiophores or cartilaginous fin-rays, 

 which lie in close apposition; in the case of the dorsal fins 

 these are calcified along their axes. At the outer ends of 

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

 Oil each side of the rays and polygonal cartilages are a 



