ANATOMY OP VERTEBRATES. 



87 



69 



69a 



Hyo-brancliijil Xranu', skull, Tiidiirile. oxxxix. 



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



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



tanelle ' above, as the basioccii^ito-sphenoid covers the hypophj^sial 



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



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



figs. 42, 22, and 69a, ?«, expand transversely as the mouth widens 



to form its fore-part, fig. 71, 



n : external to the premaxillary 



pedicles liegins the ossification of 



the turbinals. 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 



'vomerine' plate, fig. 73, I, I. 



From the membrane covering 



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



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



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



perennibranchiate Batrachia supports teeth. As the mandible, 



fig. 71, (/, lengthens, the tympanic, il). e, shortens and becomes 



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



the i)etro3al, close Ijchind, but distinct from, the tympanic. 



In the Lepidosiren the ali- and orbito-sphcnoids and the 

 tympanic remain cartilaginous ; 

 premaxillaries are represented 

 by their ascending or facial 

 parts coalesced into a single 

 l)late, sujiporting the two pre- 

 Iiensile teeth. The postorbito- 

 supcrtemporals, fig. 41, 12, are 

 ' dermal ' or scleral bones, over- 

 la2:)ping the fronto- parietals. 

 They are not present in modern Batrachia. 



In the Axolotl [Axulotes 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 masto tympanic, and is 

 separated from the alisphenoid by the large cartilaginous petrosal, 

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



hypo- 



Hyo-lir.tnchial fmiiic, slatll, older Tadpole, cxxxi 



