. Chordate morphology. Morphology (Animals); Chordata. B (V^suprabranchial I epibranchial I efferent I â ^spinoccipital foramina foramen magnum hypobronchial cerotohyal anterior ceratohyal posterior hyomandibular articulation hyomandibular branch VII â ceratobronchiol I C. lateral canal notachord canal efferent I efferent II artery Figure 5-12. Endocronium and viscerol skeleton (except jows) of Pteronisculus. A, lateral view of endocronium; B, ventral viev/; C, posterior view; D, loterol view of hyoid and first broncliial orcfies (quadrate sfiown in relation to hyomondibulo and sympletic). (Af
. Chordate morphology. Morphology (Animals); Chordata. B (V^suprabranchial I epibranchial I efferent I â ^spinoccipital foramina foramen magnum hypobronchial cerotohyal anterior ceratohyal posterior hyomandibular articulation hyomandibular branch VII â ceratobronchiol I C. lateral canal notachord canal efferent I efferent II artery Figure 5-12. Endocronium and viscerol skeleton (except jows) of Pteronisculus. A, lateral view of endocronium; B, ventral viev/; C, posterior view; D, loterol view of hyoid and first broncliial orcfies (quadrate sfiown in relation to hyomondibulo and sympletic). (After Nielsen, 1942) ences might be attributed to the jaw apparatus. The suspen- sorium, as represented by the hyomandibula, was directed posteroventrally, with the articulation process of the quad- rate well behind the vertical of the eye. The cheek was solidly covered. There was a well-developed dermohyal between the operculum and preopercle, and sometmies there were additional plates behind or below this. The bony operculum was relatively narrow, in an anteroposterior direction, and continued onto the throat as a ray-supported membrane; there was never an interopercle, although a large plate of branchiostegal origin sometimes lay below the subopercle. The intertemporal was included in the roof. In at least one genus (Moythomasia), there was a parietal foramen. The snout had a large internasal, large lateral nasals, which margined the eye (except in Cheirolepis), and generally lacked separate medial rostralsâthese were usu- ally fused with the premaxilla, though both were sometimes lacking. The eye was proportionally large, with four scle- rotic plates, and the snout short. Among what have been called palaeoniscoids, there was marked divergence from this picture. The suspensorium, as an extreme, was vertical and the cheek was free of bony plates (Dorjpterus). Reduction of many bones in size, or even their loss, is observed in several forms. In others there has been a reducti
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