4 



has extended along the terminal concave plates so as to reduce the central 

 communication to a very small foramen : osseous plates have, also, been 

 developed in the exterior hyaline cartilage : these plates are triangular, and 

 parallel with the axis of the vertebra, their apices converging towards its 

 centre : the interspaces were filled by the cartilage : and the two widest 

 (marked n, n), at the upper part of the centrum, were closed by the bases of 

 the neurapophyses. Hunterian. 



14. A vertebral centrum of a Blue Shark (Carcharias glamus). Ossification has 

 extended along the terminal articular cones so as to obliterate the central com- 

 munication and reduce the primitive notochord to a series of detached semi- 

 fluid gelatinous balls filling .the capsules that united together the opposite 

 concave surfaces of the centrums. Ossification has, also, extended through 

 the exterior cartilage, except at the parts (marked n, n) which supported the 

 neurapophyses, and at those (marked p, p) which supported the parapophyses : 

 these parts are hollow in the present dried vertebra. Hunterian. 



16. Two caudal vertebrae of the Gray Shark or Tope (Galeus communis), showing a 

 similar progress of ossification of the bodies : the neural canal is protected not 

 only by the proper neurapophyses, but by interneural plates resting upon the 

 interspace of the vertebrae : the haemal arches are slender, and there is a single 

 pair for each centrum. , Hunterian. 



B. Characteristic ossified vertebra of the different classes of Vertebrata. 



16. Five vertebras of a bony Fish, vertically bisected, showing the articular cavities 



formed by the opposite terminal conical surfaces. Each vertebral centrum 

 has a very deep and large depression opening behind the parapophyses ; there 

 are smaller depressions at the base of the neurapophyses. Hunterian. 



17. A caudal vertebra of an Angler (Lophius piscatorius). The concave articular 



ends of the centrum, characteristic of the vertebrae of Fishes, are formed by 

 smooth compact bone ; the exterior of the centrum consists of light reticular 

 osseous texture, continued from the neural arch above to the haemal arch be- 

 low : both arches have coalesced with the centrum. Hunterian. 



