ANATOMY OF VEETEBEATES. 



87 



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

 afterwards the frontals, ib. ib., n, 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 69a, n, expand transversely as the mouth widens 

 to form its fore-part, fig. 71, 

 n : external to the premaxillary 

 pedicles begins the ossification of 

 the turbinate. The 'pterygoid 

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

 inner side of the hypotympanic, 

 29, and forward to the ' palatine ' 

 bone, and the bifid dentigerous 



69 



69a 



' vomerine ' 



fig. 



73, /, /. 



Hyo-branehial frame, skull, Tadpole, cxxxix. 



covering- 



plate, 

 From the membrane 

 * Meckel's cartilage,' figs. 69a and 70, d, are exclusively developed 

 the mandibular elements, the s angular,' fig. 43, 30, and ' 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 two pre- 

 hensile teeth. The postorbito- 

 supertemporals, fig. 41, 12, are 

 ' 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 condyle, 

 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, 



Hj-o-br.anchial frame, skull, older Tadpole, cxxxi 



