. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. DIPNOI. 269 arthrodira, they are few. In the existing species parasphenoid, vomers, palatoquadrate and squamosal, as well as dentary, angu- lar and opercular in the lower jaw, are more or less certainly to be recognized ; but beside these there are several bones in the cranial roof which are not to be homologized with those in other groups. The operculum is supported by bones (operculum, inter- operculum), and the hyoid and (four or five) branchial arches are cartilaginous. The pectoral and pelvic arches are cartilaginous, t
. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. DIPNOI. 269 arthrodira, they are few. In the existing species parasphenoid, vomers, palatoquadrate and squamosal, as well as dentary, angu- lar and opercular in the lower jaw, are more or less certainly to be recognized ; but beside these there are several bones in the cranial roof which are not to be homologized with those in other groups. The operculum is supported by bones (operculum, inter- operculum), and the hyoid and (four or five) branchial arches are cartilaginous. The pectoral and pelvic arches are cartilaginous, the former with membrane bones of the fish-type (p. 174) weakly developed. The pelvis consists of a median plate with (in recent forms) three anterior horns. The fins themselves are very prim- itive, and consist of an axial portion, from which, in Ceratodus, biserial cartilaginous fin rays arise. In many fossils the ante-. FlG. 270. Restoration of Dinichthys, from Dean. rior part of the body is enclosed in a strong armor of bony der- mal plates, there being a hinge between the dorsal plates and the base of the skull. The brain differs from that of the teleostomes in the ner- vous character of the cerebral mantle. The two hemispheres are united in Ceratodus, but in Protopterus they are distinct back to the anterior commissure. The mid brain is paired in Ceratodtis, simple in Protopterus; the cerebellum is but a small transverse fold. The pineal structures have a long stalk, while the envel- opes of the brain are richly developed, and in Protopterus these enter above the fossa rhomboidalis into close connection with the endolymphatic system of the ear. An optic chiasma is present. The teeth are few in number, and are apparently formed by the fusion of several primitive teeth. Of these there is a pair of larger grinding plates borne on the palatopterygolds, a much. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readabi
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