| OCR Text |
Show 1904.] OSTEOLOGY OP THE ELOPDLE AND ALBULIDAE. 79 branchials are set close together, without the usual interval. The fourth and fifth basibranchials are represented by an undivided plate of cartilage, as is customary in Teleostean fishes. No trace of ossification is_ to be detected in this plate, a fact which is of interest m relation to the discovery by S winner ton of separate ossified fourth and fifth basibranchials in that aberrant and specialised genus Cromeria (Zool. Jahrb., Abth. f. Anat. xviii. 1903, p. 66). The hypobi anchials are much reduced in the Mormyroids, and, as already pointed out, the second hypobranchials are confluent with prominent tendon-bones. In Coilia and Engraulds the second hypobranchials are fused with the sides of the second basibranchial, and in Chanos the third hypobranchials are fused with the third basibranchial, but in each case the suture remains visible. The " spicular bone " is generally taken to represent the modified first pharyngobranchial. In Hyodon the first pharyngobranchial bone is large, and is certainly upturned and rod-like, resembling a spicular bone ; but in all the forms examined which have a true spicular bone this arises from the upper surface of the first epibranchial, and not from its anterior end as it does in Hyodon. In Chirocentrus the first pharyngobranchial is a conical bone projecting forward and upward. In AIbula it is a bone which runs forward with its axis in a line with that of the first epibranchial, and is clearly serially homologous with the second and third pharyngobranchials. In Mormyrus and Mormyrops, also, there is a small ossified first pharyngobranchial, but as a rule this element of the visceral skeleton is cartilaginous. The above-mentioned genera appear to have no true spicular bone, but in Engraulis, Clupea, Chatoessus, and Chanos there is a cartilaginous first pharyngobranchial and a true spicular bone in addition, while in Elops, Megalops, and Alepocephalus there is a well-defined and fully ossified first pharyngobranchial as well as a slender spicular bone. The simultaneous presence of a spicular bone and an unmistakable first pharyngobranchial bone effectually disposes of the argument that the spicular bone represents a modified first pharyngobranchial. The spicular bone has the value of an ossified ligament for the attachment of the branchial skeleton to the side of the pro-otic, and is not a primary constituent of the visceral skeleton. The confusion which has arisen with respect to it, is probably due to the fact that in some cases-it is not yet possible to say whether they are many or few- the first pharyngobranchial takes upon itself the suspensory function of the real spicular bone. The long bone which in the Berycidse and Oyttidse is attached to the anterior end of the first epibranchial appears to be a true first pharyngobranchial, but further observations upon the relations and the development of this bone are much to be desired. It is frequently difficult to say whether a bone of the branchial skeleton is really toothed or not, since in cases where teeth are |
