54 LECTUKE III. 



In the southern Chimfera ( CallorhyncJmsi) a greater proportion of 

 the chorda dorsalis is composed of the dense fibrous capsule, but it 

 shows no trace of annular structure. In the northern Chimajra, 

 according to Miiller (xxr. p. 68.), another stage towards the forma- 

 tion of vertebral bodies begins to manifest itself by slender sub- 

 ossified rings in the cartilaginous sheath of the chorda dorsalis, 

 which, however, are more numerous than the neural arches. The 

 neurapophyses and the bases of the transverse processes of about ten 

 of the anterior vertebrae coalesce, in all the Chimajrge, to form a 

 continuous accessary covering of the fore part of the chorda ; and 

 the confluent neural sj)ines here form a broad and high compressed 

 cartilaginous plate. In the remainder of the vertebral column the 

 neural arches are distinct from the transverse processes (parapophyses), 

 and from the htemal arches, which these constitute in the tail. 

 Between each neurapophysis an accessary cartilaginous interneura- 

 pophysis* is wedged. 



Amongst the Sharks (^Sqnalidce) a beautiful progression in the 

 further development of a vertebra has been traced out, chiefly 

 by J. Miiller (xxi. p. 64.). In Heptanchus {^Squalus cinereus) the 

 vertebral centres are still feebly and vegetatively marked out by 

 numerous slender rings of hard cartilage in the capsule, the number 

 of vertebras being more definitively indicated by the neurapophyses 

 and parapophyses ; but these remain cartilaginous. Interneural 

 pieces are wedged between the neural arches, and close them above ; 

 the pleurapophyses are similarly wedged into the interspaces of the 

 parapophyses, and articulate directly with the vertebral bodies, f In 

 the Piked Dog-fish (Accmthias) the vertebral centres coincide in 

 number with the neural arches, and are defined by a thin layer of 

 bone, which forms the conical cavity at each end, but the rest of the 

 vertebra remains cartilaginous. In the Spotted Dog-fish (Sci/llium) 

 the whole exterior of the centrum is covered by soft cartilage, except 

 at the concave ends, where the two thin funnel-shaped plates of os- 

 seous matter coalesce at their perforated aj)ices, and form a basis of the 

 vertebral body like an hour-glass ; the series of these centrums 

 protecting a continuous moniliform chorda dorsalis. In the great 

 Basking vShark (Selache) the vertebral bodies are chiefly established 

 by the terminal bony cones, the thick margins of which give 

 attachment to the elastic capsules containing the fluid remains 

 of the gelatinous chorda, which now tensely fills the interver- 



* " Ossa intercalaria cruriim," " Laminm intercrurales" {^I'nWcr). 



f Traces of the vegetative repetition of vertebral elements may be seen in the 

 higher animals : the interparietal bone of the Rodents is the ' os intercalare spinale ' 

 of the second cranial vertebra, and the ossa Wormiana are ' ossa intercalaria,' as 

 John Miiller has well remarked in his memoir on Myxinoids, p. 92. 



