90 ANATOMY OF VERTEBRATES. 



exoccipitals have coalesced with the superoccipital above, and with 

 the basiocci23ito-sphenoidaI plate below ; this latter, fig. 98 A, sends 

 out on each side a process to form the floor of the otocrane, and its 

 forward extension is long and narrow : the tympanic develop>es a 

 frame for the large ear-drum, fig. 44, N : the stapes, now colu- 

 melliform, stretches from that membrane to the foramen of the 

 labyrinth. 'Meckel's cartilage,' figs. 69 and 71, d, contributes 

 nothing to the bony conductor of sonorous vibrations which 

 becomes subdivided into a chain of ossicles in Mammalia. The 

 hypotympanic, fig. 44, 2s, sends forward a process to the end of 

 the maxillary, thus articulating, as in the Plagiostomes, with both 

 upper and lower jaws. The essential or neurapophysial parts of 

 the p)refrontals encompass the prosencephalon, and coalesce to 

 form a ring of bone, like the exoccipitals : it is the ' os en 

 ceinture ' of Cuvier,' part of which appears at the upper surface 

 of the cranium, fig. 44, u, between the frontals and antorbitals, 

 ib. 15, which here, and still more in the Toad, assume the 

 character of nasals connate with lacrymals. Between these and 

 the premaxillaries are the small bony parts of the olfactory sacs, 

 usually described as ' nasal bones.' The orbital and temjroral 

 fosssc form one wide common vacuity on each side the cranium : 

 it is divided from the nostril by the junction of the maxillary, 

 ib. 21, with the naso-lacrymal bone : the premaxillaries, ib. 22, 

 are small bones, with a well-marked facial and buccal portion. 

 The palatines, fig. 98, A, are transversely extended : the divided 

 vomer is dentigerous : the pterygoid, ib. 24, sends out three rays 

 for the splienoidal, tympanic, and palato-maxillarj^ connections re- 

 spectively. The mandible is edentulous. The hyoid arch with 

 its branchial appendages has clianged its connections as well as 

 shape. In the tadj)ole, with the fully-developed gills, the carti- 

 lage representing the stylo- and cerato-hyals, figs. 69 and 6 9 A, a, is 

 short and thick, and attached to the back of the tympanic pedicle, 

 ib. e, to the end of which is articulated the mandible, ib. d. The 

 ceratohyals are connected below to a median piece, ib. b, which may 

 represent both the basihyal and basibranchial: it directly supports 

 the hypobranchials c, c, to which the ceratobranchials, or branchial 

 arches are attached. As the gills wither, the stylo-ccratohyals, figs. 

 70 and 71, a, lengthen, attenuate, and acquire an independent 

 attachment to the petrosal ; the basi- and hypo-branchlals, fig. 

 74, c, c, coalesce into a single cartilaginous plate, with the 

 ' basihyal,' ib. b ; and the ceratobranchials arc reduced to a single 

 pair, which represent the so-called ' posterior cornua ' of the hyoid. 



' cxxxix. torn V. pt. 2, p. 389, pla. xxiv.— xxvii., well illustrate the osteology of 

 the Batrachia. 



