| OCR Text |
Show 42 DR. W. G. RIDEWOOD OX THE CRANIAL [May 3, basibranchials is roughly hexagonal in shape, elongated in an antero-posterior direction, and continued posterioi'ly into a sinal rod of cartilage which lies freely between the fifth cerato-branchials. The dentigerous plates on the fifth ceratobranchials are readily removable, which is not usually the case. I here is a true ossified first pharyngobranchial, projecting slightly upwards by the sideo the parasphenoid, in addition to the small spicular bone, which m Teleosteans generally has been erroneously taken to represent the first pharyngobranchial. The spicular bone stands upright from the antero-superior extremity of the first epibranchial, and selves Text-fig. 11. eb*' ( I xcb5 JSlops saurus, hyobranchial skeleton, dorsal view. The epibrauchials and pharyngobranchials of the right side are not shown. For explanation of lettering, see p. 81. to attach the branchial skeleton to the pro-otic bone at the point where the latter meets the opisthotic bone. The fourth pharyngobranchial is cartilaginous, and is flanked on its pharyngeal surface by a dentigerous membrane-bone exactly similar to those which occur on the second and third pharyngobranchials. Even the first pharyngobranchial bears a small dentigerous plate in its posterior part. The transition from these dentigerous plates to the small toothed plates that accompany the gill-rakers on the epibrauchials is quite gradual. The whole hyobranchial skeleton gives one the impression that it is in a very simple and unmodified condition. |
