048 DR JAMES STARK ON THE EXISTENCE OF AN OSSEOUS STRUCTURE 



Now, it is worthy of remark that these strengthening pillars represent exact- 

 ly the analogous supporting columns of the vertebral cups of the osseous fishes. 

 Indeed, deprive the vertebrae of many of the osseous fishes of their spinous pro- 

 cesses (those of the Haddock for example), and it will appear evident to every one 

 that these supporting columns are not only of equal number, but subserve the 

 same useful purposes, in both classes of fishes. 



In the Rays, every space between the supporting columns is filled up by car- 

 tilaginous matter, so as to cause the body of each vertebra to assume the form of 

 a short cylinder ; and it is this cartilaginous envelope which has hitherto prevent- 

 ed the above described osseous structure from being recognised. 



In almost all the vertebrae, however, there is an additional means used to 

 strengthen the osseous cups, and prevent them from being fractured in violent 

 motions of the animal. It is well known that cartilaginous, like other fishes, 

 possess only a limited power of flexing the spinal column in a perpendicular 

 direction. The generally square or triangular form of the cartilaginous envelopes 

 of the vertebrae, but especially their large interlocked processes, effectually pre- 

 vent much power of flexion in a perpendicular direction. Lateral motion, how- 

 ever, is freely allowed ; and as we have seen that the lateral osseous supporting 

 columns do not strengthen above half the diameter of the cups of the vertebrae, 

 had no other means been used, there might have been some chance of the verte- 

 brae giving way in this direction, during violent motions of the animal. This, 

 however, is guarded against by a most beautiful arrangement. 



From the lateral edges of the cup-shaped bodies arise from two to six or 

 more processes of true bone, which, however, after extending a very little way to 

 meet those from the opposite cup of the same vertebra, are continued as a chain 

 of calcareous granular particles, resembling those forming the calcareous encrust- 

 ations of the skeleton (Fig. 6, a). Between these are Fig 6 

 frequently remarked lines of square calcareous granules 

 running in the same direction viz., from the outer 

 margin of the upper cup to that of the lower cup of the 

 same vertebra. This arrangement, consequently, forms 

 a series of supporting pillars, partly osseous and unyielding, partly composed of 

 yielding jointed particles. As these jointed lateral supports are attached to the 

 margin of the cups, while the lateral solid columns above described do not ex- 

 tend over more than from a third to a half of the outer surface of the cup, a free 

 space intervenes between these two kinds of support, a space filled up in the 

 recent vertebra with cartilaginous matter. (Fig. 7.) 



This apparatus seems beautifully adapted to the purpose of 

 allowing a great amount of lateral motion without endangering the 

 rupture of the vertebrae. The shortness of the internal solid osseous 



