ANATOMY OF VERTEBRATES. 



87 



69 



69A 



Hyo-branckial frame, skull, Tadpole, cxxxix. 



hypotympanic, fig. 43, 29. The parietals, ib., 44 and 68, 7, and 



afterwards the frontals, ib. ib., 11, progressively cover the 'fon- 



tanelle ' above, as the basioccipito-sphenoid covers the hypophysial 



vacuity below. An antorbital plate, fig. 72, b, extends from the 



frontal to the maxillary. The premaxillaries, at first beak-shaped, 



figs. 42, 22, and 6 9 A, n, expand transversely as the month widens 



to form its fore-part, fig. 71, 



n : external to the premaxillary 



pedicles begins the ossification of 



the turbinals. The tf pterygoid 



plate,' fig. 43, 24, extends to the 



inner side of the hypotympanic, 



29, and forward to the ( palatine ' 



bone, and the bifid dentigerous 



6 vomerine ' plate, fig. 73, Z, /. 



From the membrane covering 



( MeckePs cartilage,' figs. 69A and 70, d, are exclusively developed 



the mandibular elements, the ( angular,' fig. 43, so, and f dentary,' 



ib. 32, being the chief; there is also a ' splenial,' which in some 



perennibranchiate Batrachia supports teeth. As the mandible, 



fig. 71, d, lengthens, the tympanic, ib. e, shortens and becomes 



more vertical, and the hyoid arch, ib. a, shifts its attachment to 



the petrosal, close behind, but distinct from, the tympanic. 



In the Lepidosiren the ali- and orbito-sphenoids and the hypo- 

 tympanic remain cartilaginous ; 

 premaxillaries are represented 

 by their ascending or facial 

 parts coalesced into a single 

 plate, supporting the tw T o pre- 

 hensile teeth. The postorbito- 

 supertemporals, fig. 41, 12, are 

 6 dermal ' or scleral bones, over- 

 lapping the fronto-parietals. 

 They are not present in modern Batrachia. 



In the Axolotl (Axolotes marmoratus), the basioccipital is repre- 

 sented by the posterior part of the common broad and flat basi- 

 cranial bone. The exoccipitals are separated below by this process, 

 and above by a cartilaginous representative of the superoccipital. 

 Each exoccipital developes a small, almost flattened coiidyle, 

 anterior to which it is perforated by the eighth pair of nerves ; it 

 articulates above with the parietal and mastotympanic, and is 

 separated from the alisphenoid by the large cartilaginous petrosal, 

 to which a small discoid representative of the stapes is attached, 



71 



Hyo-braucliial fi-ame, skull, older Tadpole, cxxxi 



