The Structure and Development of the Caudal Skeleton of the Teleostean Fish, Pleuragramma antarcticum.

• Published in: Proceedings of the Zoological Society of London
• Main Author: Totton, A. Knyvett
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1914
• Subjects: Antarc*
• Online Access: http://dx.doi.org/10.1111/j.1469-7998.1914.tb07034.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1469-7998.1914.tb07034.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-7998.1914.tb07034.x; https://zslpublications.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-7998.1914.tb07034.x

Summary. The development of the vertebral column begins at the caudal end, the hypaxial elements being the first to appear. This coincides with a down‐bending of the notochord (compare with this the analogous condition of the vertebral column in the Ichthyosauria). Epaxial elements do not appear until this condition has given way to the straight condition again. Arches appear as paired cartilages at the sides of the caudal artery and vein and of the nerve‐cord. They are separated from the notochord by connective tissue. The notochord is of a relatively enormous size, and persists with only slight constriction throughout life. The centra consist of thin papery lamellæ of membrane‐bone. Ossification is generally weak. The neural and hæmal arches of the penultimate centrum are double, owing to the splitting of single rudiments. Similar phenomena are to be observed in other fishes. They may be produced by different causes:— (1) Splitting of an originally single rudiment. (2) Crowding of two arches on to one centrum. (3) Fusion of the first epiural apophysis with the last neural arch. (4) Exceptional equal development of both arch and intercalary. (5) Secondary diplospondyly, i. e. fusion of two centra. Large cartilages are present above and below the last two centra in the adult, which support a dorsal and a ventral series of procurrent fin‐rays. Their great size is probably connected with the weakness of general ossification. The hypural bones of the adult are formed by a fusion of hæmal arches and radials. This compound nature of the hypurals may be seen anteriorly in adult Selachians and in the Sturgeon, but it has not been shown before, as far as I am aware, in Teleosts.