. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 82 COMPARATIVE MORPHOLOGY OF VERTEBRATES. AMPHIBIA.—Several points distinguish the amphibian from other skulls. The chondrocranium is platybasic (p. 61); except for a small synotic tectum frequently present, it is not roofed by cartilage; the otic capsule has a fenestra vestibuli occu- pied by the stapes, a development connected with the power of hearing (p. 73); there are two occipital condyles; and the quadrate is immovably united to the cranium by two processes, an otic process, joining the otic capsule, and
. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 82 COMPARATIVE MORPHOLOGY OF VERTEBRATES. AMPHIBIA.—Several points distinguish the amphibian from other skulls. The chondrocranium is platybasic (p. 61); except for a small synotic tectum frequently present, it is not roofed by cartilage; the otic capsule has a fenestra vestibuli occu- pied by the stapes, a development connected with the power of hearing (p. 73); there are two occipital condyles; and the quadrate is immovably united to the cranium by two processes, an otic process, joining the otic capsule, and an 'ascend- ing process' which reaches the upper margin of the trabecula, and which, in many reptiles, often ossifies as the epipterygoid FIG. 82.—Chondrocranium of Amphiuma, lateral and dorsal views, aop, antorbital process; ap, ascending process of quadrate (epipterygoid); ct, cornua trabeculae; de, foramen, for ductusendolymphaticus;e/>, ethmoid plate; fo, fenestra vestibuli; m, Meckel's cartilage; n, notochord; oc, olfactory capsule; ov, occipital vertebras; p, parachordal; q, quadrate; s, stapes; t, trabecula; 2-8, nerve exists. The cartilage cranial bones are few. Usually only exoccipitals are developed in the hinder region, while the rule is a single petrosal (prootic), but occasionally epi-, opisth-, and pterotic occur. There is but a single pterygoid, while basi-, pre-, and alisphenoids are not ossified. The membrane bones in existing amphibians have separated from the integument and have sunk to a deeper position than in fishes, but in the stegocephals the presence of grooves for the lateral line system would indicate a close connexion between skin and bones. In the latter group the membrane bones are numerous, but in existing species they are noticeably reduced. Except in stegocephals and the caecilians there are large vacuities in both floor and roof of the skull. The lower jaw also has a reduced number of bones, there being at most five including the
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1912
