| OCR Text |
Show 1894.] HYOIP ARCH OF CERATODUS. 639 ligament, more strongly developed than in Ceratodus, running upwards and inwards from the upper and inner end of the ceratohyal to the base of the skull at the side of the parasphenoid. There is no basihyal nor hypohyal, but the lower ends of the ceratohyals are connected by ligament. N o cartilage which might correspond with the hyomandibular of Ceratodus is to be distinguished. O w e n (7), evidently describing an improperly articulated skull, writes: " a strong cylindrical and almost straight styloid bone is articulated by a somewhat compressed and expanded upper extremity to the cartilaginous petrous element of the temporal; it extends downwards and forwards, parallel with the os tympanicum1 and is articulated to the upper part of the expanded posterior extremity of the ceratohyoid bone." The ceratohyal is named correctly, but is unfortunately articulated with the lower end of the cranial rib, which, in the figure, is made to point forwards instead of backwards and is called " styloid." Writing later (8) in 1866 he adopts Bischoff's (1) view that this latter bone is the suspensor of the pectoral girdle, for, in his fig. 41. no. 51, it is called scapula and is articulated at its lower end with the shoulder-girdle, which is called coracoid. Two years later Parker (9) described it as the first pharyngo-branchial; and it was left to Giinther (4) in 1871 to demonstrate that this bone, which had suffered such vicissitudes of^nomenclature, is simply the first rib which has acquired a secondary connection with the skull. There are no careful descriptions of the hyoid arch of Lepidosiren, but it may be concluded that it differs but little from that of Protopterus. Briihl (2) (Taf. lxiii. Fig. 8, Punkt 2) speaks of an articular cavity in the postero-external border of the chondrocranium for insertion of the hyoid apparatus ; and Hyrtl (6) states that the hyoid is attached to a blunt process of the quadrate, and that the ventral ends are united by a rigid synchondrosis and not by a ligament as in Protopterus. Giinther (4, p. 526) mentions the absence of basihyal and glossohyal (i. e. the elements named in this article the hypohyal and basihyal). W e may, happily, n o w look forward to more minute descriptions of the visceral skeleton of this once rare Dipnoan in the publications of the numerous investigators wdio are prosecuting their researches on the specimens recently collected by Dr. Bohls in Paraguay. A careful examination of the hyoid system of living Dipnoi leads one to conclude that there is no connection between the reduction of the hyomandibular in these fishes and its adaptation as a secondary suspensorium in the Elasmobranchii (excluding the Holocephali) and the osseous fishes, and there appears to be very httle evidence in support of Gadow's view (3, p. 459) that the reduction of the Pre-opercular. |
