THE SKULLS OF FISHES AND AMPHIBIA. 207 



The cartilaginous basis of h is strengthened by eight bones, 

 four on each side. Of these, two lie altogether external to the 

 cartilage, and leave between themselves and it an interspace, in 

 which the levator muscle of the lower jaw lies. 



The other pair consist, firstly, of a large bone, which lies, 

 for the most part, internal and inferior to the cartilage, and 

 extends from the inner side of the articular process for the lower 

 jaw, upwards and inwards, to meet its fellow, posteriorly ; for- 

 wards, to articulate with the anterior of the external bones. 

 And, secondly, of a small bone fitted on to the anterior and 

 external edge of this, and to the inferior surface of the anterior 

 external bone. The whole apparatus, h, is very loosely con- 

 nected with the skull, so that it is capable of being protracted 

 and retracted with great freedom. 



The general relations of this singular mechanism to the 

 manducatory organs of ordinary Teleostean fishes appears to be 

 rendered evident by the same method as that which has been 

 employed to demonstrate the nature of the jaws of the Plagio- 

 stomes. The osseo-cartilaginous structure, 7c, answers to the 

 palato-quadrate arch of the Sharks and Kays, or to the palato- 

 quadrate cartilage of the embryonic fish ; and /, g, h corre- 

 spond with the undivided suspensorium of the Sharks and Rays, 

 and with the hyomandibular and symplectic cartilages of the 

 embryo Teleostean. Furthermore, on comparing h with the 

 maxillary apparatus of Sjmtularia, the cartilaginous basis appears 

 to answer to the cartilages (D, D) of that fish joined together ; 

 while the anterior outer bone in the Sturgeon is the equivalent 

 of the bone E, and may be regarded as a maxilla. The two 

 internal bones correspond with the inner bone of the Spatu- 

 laria's jaw. The Sturgeon, however, more nearly approaches 

 ordinary fishes in the development of an anterior or palatine 

 element, distinct from the posterior or pterygoid element. As 

 for the small external bone, which passes obliquely from the end 

 of the maxilla to the outer surface of the cartilage, it is possibly 

 a quadrato-jugal. 



D. The cranium consisting of cartilage to a greater or less 

 eitent, but with cartilage bones as well as membrane bones. — ■ 



