THE GANOIDEI. 125 



structure. The suspensorium consists of two ossifications 

 united by a cartilaginous intermediate portion. The upper — 

 broad, and movably articulated with the periotic capsule — is 

 the hyomandibular ; the lower answers to the symplectic of 

 osseous fishes. The cartilaginous palato-quadrate arcade is, in 

 part, replaced by a series of bones : the palatine lies in front, 

 and is connected with the prefrontal region of the skull ; be- 

 hind it, lie representatives of the pterygoid, the metapterygoid, 

 the ectopterygoid ; and, most posteriorly, of the quadrate 

 bone. The last furnishes a condyle to the articular element 

 of the mandible. The symplectic is either loosely connected 

 with the quadrate, as in Lepido&Uus. or more closely united 

 with it, as in the other genera. 



In Lepidosteus and Amia, a f.trcng and long membrane 

 bone, the preopercidum^ is developed on the outer side of the 

 hyomandibular and quadrate bones, and connects them still 

 more firmly together. 



The maxilla is represented by a series of small separate 

 ossifications in Lepidosteus. The proximal end of the man- 

 dibular cartilage ossifies, and becomes a distinct articidare. A 

 dentary element is added on the outer, and a splenicd one 

 upon the inner side of the cartilage ; and in Lepidosteus, an- 

 gidar, supra-angular, and coronary elements are added, so 

 that the components of the mandible are as numerous as in 

 reptiles. Lepidosteus and Amia have branchiostegal rays, 

 but Polypterus has none — at any rate, of the ordinary kind. 

 A single jM^M/ar plate is developed between the rami of the 

 mandible in Amia, and there are two such plates in Polypterus, 

 which may possibly represent branchiostegal rays. 



In A(:cip>enser, Spatularia, and Amia, the pectoral arch 

 presents two constituents : one, internal and cartilaginous, 

 answers to the cartilaginous pectoral arch of the JElasmo- 

 branchii, and to the scapula and coracoid of the higher Ver- 

 tehrata ; the other, external, consists of membrane bones rep- 

 resenting the clavicular, supra-clavicular, and post-clavicular 

 bones of the Teleostei. In Lepidosteus one centre of ossifica- 

 tion appears in the cartilage ; in Polypterus, two. The upper 

 represents the scapula, and the lower the coracoid. 



It has been already stated (p. 38) that Polypterus comes 

 nearest to the Elasmobranchii in the structure of the rest of 

 the limb. The numerous dermal fin-rays, all nearly equal in 

 size, are connected with the rounded periphery of the broad 

 and elongated disk formed by the skeleton of the fin ; and the 

 scaly integument is continued to the bases of the fin-rays, 



