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British Colonial Observatories, under the Departments of the 

 Ordnance and Admiralty. Printed by the British Govern- 

 ment, under the superintendence of Lieutenant-Colonel Sabine, 

 of the Royal Artillery. Part 1. 1840-1841. — By the Master- 

 General of the Ordnance. 



Monday, \^th March 1844. 



Dr ABERCROMBIE, V.P., in the Chair. 

 The following communications were read : — 



1. On the Existence of an Osseous Structure in the Vertebral 

 Column of Cartilaginous Fishes. By James Stark, M.D., 

 F.R.S.E. 



The author, after quoting from the works of writers on Ichthyology 

 and Comparative Anatomy their descriptions of the vertebral columns 

 of cartilaginous fishes, proceeded to point out the existence of an 

 osseous structure in the vertebrae of the Plagiastonii, or Rays and 

 Sharks. In these animals the essential portion of each vertebra 

 consists of a double cup or saucer-shaped osseous piece, resembling in 

 form and structure the double cup-shaped vertebrae of osseous fishes, 

 being, like them, composed of concentric rings of osseous matter. It 

 was shewn that the whole of the encrustingr cartilaginous matter, with 

 its calcareous granules, could be removed from this osseous structure, 

 without affecting the integrity of the spinal column, or interfering with 

 the intervertebral ligamentary apparatus which was alone attached to 

 this osseous structure. These double cup or saucer-shaped vertebra; 

 were in the Rays shewn to be perforated by an extremely minute 

 central aperture, which was, however, of a considerably larger size 

 in a few genera of Sharks, as in the Dog-fish ; while in others, as in 

 the Saw-fish, no such aperture could be distinguished. 



These double cup or saucer-shaped vertebrae receive various 

 strengthening columns, pillars, or plates of osseous matter, which 

 differ in structure and disposition in the several genera and species 

 of cartilaginous fishes. In some, these plates were shewn to have a 

 concentric arrangement, and to be separated from each other by plates 

 of cartilage. In others, the plates were broad and flat, and extended 

 only from the margin of the one cup to that of the other cup of the 

 same vertebra. In others, the supports were compound and broad 



