422 ON THE ORKNEY ANIMAL. 



to this bail and socket joint even in the human 



species ; and, therefore, when the humours be- 

 come scanty, as in old age, the vertebra: approach 

 on the sternal aspect, the spine grows shorter, and 

 is b?nt forward. The spine is shortened, too, by 

 a long continuance in the erect posture, which 

 compresses the intervertebral cartilages, opposes 

 the influx, but favours the efflux or the absorp- 

 tion of the intervertebral fluids. A closer analogy, 

 lidweVerj to this ball and socket joint of fishes, is 

 to be found in different quadrupeds ; and a near 

 resemblance to the ball and socket joint of art, 

 miy he seen in the articulation of the femur with 

 th e pelvis, and of the humerus with the scapula, 

 in man, and most quadrupeds, — in all the verte - 

 bra? of ue viper, and in the cervical vertebra? of 

 t&e horse. 



The fluid is supplied by exhaling arteries, and 

 in these vertebrae the arteries seem to have en- 

 tered by the sulci or fissures. The interstices 

 between the cylinders were filled with a fluid not 

 UiiliMe in colour to that of the joint, but, in point 

 of consistency, more resembling a jelly. This 

 fluid escapes, as well as that of the joint, by eva- 

 poration y and this evaporation is the cause that 

 the space between the cylinders appears empty in 

 the dried vertebrae. 



The whole osseous part of these vertebra? is un- 

 commonly soft and porous ; and as the cartilagi- 

 nous part predominates, the dimensions of the 

 vertebra? are considerably diminished when they 



