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  Section: Anatomy of Vertebrate Animals » The Class Amphibia
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In the Proteidea


In the Proteidea there are three or four branchial arches, each usually consisting of two cartilaginous, or ossified, pieces on each side. In the Salamandridea, there are, primitively, four branchial arches, but of these, portions of only the two anterior remain in the adult. Four are developed in the Caecilia, and three of these are permanent.

Some peculiarities exhibited by the skulls of the Gymnophiona, and by the Labyrinthodonta, are worthy of especial notice.

In the former, e. g., in Ichthyophis glutinosa, the skull is covered by a complete bony roof, formed, mainly, by the exoocipitals, parietals, frontals, prefrontals, nasals, and ascending processes of the premaxillaries. Between the ex-occipitals, the parietal, and the frontal, above, the maxilla, in front, and the quadrate, behind and below, lies a bone which appears to answer to the bone (z) of the Frog, and to its quadrato-jugal. Between the nostril and the maxilla, the nasal bone and the premaxi la, there is a bone which seems to be an ossification of the cartilaginous ala nasi.

Another bone nearly encircles the orbit, and, as a supra - and postorbital bone, has no analogue among existing Amphibia.
Side and upper views of the skull of Trematosaurus. The sculpture of the cranial bones is not represented in the lower half of the upper view of the skull, in order to show the sutures more distinctly
Fig. 56. - Side and upper views of the skull of Trematosaurus. The sculpture of the cranial bones is not represented in the lower half of the upper view of the skull, in order to show the sutures more distinctly.
The palatine bones surround the posterior and outer margins of the posterior nares, and then extend back on the inner side of the maxilla, in a manner unlike any thing observed among other existing Amphibia. But in the Labyrinthodonta, both this disposition of the palatine and the complete roofing over of the skull by bone are repeated, and there is a postorbital bone.

The Labyrinthodont skull is further characterized by the development of distinct pointed epiotics, like those of fishes, and of paired ossifications, which take the place of the supraoccipital, as in many Ganoidei. In many Labyrinthodonts the articular element of the lower jaw is completely ossified.

Archegosaurus possessed branchial arches when young, and there can be little doubt that the other Labyrinthodonts resembled it in this respect.

The limbs and their arches are completely absent in the Gymnophiona, and, apparently, in the extinct Ophiderpeton of the Carboniferous formation. In all other Amphibia the pectoral arch and limbs are present, and, in all but Siren, the pelvic arch and limbs. The anterior and posterior limb-arches consist of a continuous cartilage on each side, divided by an articular surface into a smaller dorsal moiety, and a more expanded ventral portion. The dorsal moieties are, respectively, the scapula and the ilium. The ventral moieties are divided by notches, or fontanelles, into two portions - an anterior, precoracoidal, or pubic part, and a posterior, coracoidal, or ischial part.


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