54 FOSSIL REPTILIA OF THE LONDON CLAY. 



cavity in the. atlas for the occipital tubercle : below this is the surface for the detached 

 hypapophysial part of the atlas (fig. 39, h) and above and behind it are the two 

 surfaces for the atlantal neurapophyses ; the whole posterior surface of the odontoid 

 is anchylosed to the proper centrum of the axis. 



The neural arch of the axis developes a short ribless diapophysis from each side of 

 its base ; a short zygapophysis (z), from each side of its anterior border ; a thick sub- 

 bifid zygapophysis (/) from each side of the posterior border, and a moderately long 

 retroverted spine (ns) from its upper part. The centrum terminates in a ball behind, 

 and below this sends downwards and backwards a long hypapophysis {Jtx). 



In the skeleton of an African Constrictor {Python regius, Dum.), which measured 

 15 feet 6 inches in length, there are 348 vertebrae, of which the 279 following the atlas 

 and axis support simple moveable ribs ; of these vertebrae about 70 anterior ones have 

 long hypapophyses, as in fig. 4, h, T. XIV, which in the rest subside to the obtuse ridge 

 and tubercle, as in fig. 1, h, T. XIII : the caudal vertebra? have not the ribs moveably 

 articulated ; they are 67 in number ; of these vertebras 56 have bifurcate hypapophyses 

 as in fig. 42, //, T. XIV; the six anterior caudalshave bifurcate ribs (ib., fig. 4\,pl), in 

 the rest they are simple (ib., fig. 42, pi), and lengthen out the diapophyses (ib. d,) to 

 which they are anchylosed. 



The ribs or the trunk- vertebrae, like those of the tail, are ' pleurapophyses' or ' verte- 

 bral ribs ;' there are no ' haemapophyses' or sternal ribs ; the exogenous hypapophyses 

 (h, fig. 42) take the place of the haemapophyses in the tail. The pleurapophyses of 

 the trunk (T. XIII, figs. 2', 3'), are long, slender, curved, subcompressed, expanded at 

 the proximal end, which presents an articular surface chiefly concave, and adapted to 

 the diapophysial tubercle {d, figs. 2, 3,) above described ; there is a rough depression 

 on the fore part of the expansion for the insertion of a ligament, and a tuberosity 

 projects from the upper and back part ; the distal end of the rib is truncate, with a 

 terminal pit ; a medullary cavity extends through a great part of the length of the rib, 

 as shown in fig. 3". 



There is a small cavity in the substance of each neurapophysis, which communicates 

 by a smaller foramen with the zygantrum. A vascular cavity in the centrum com- 

 municates with the neural canal. 



In the skeleton of a Tiger-boa (Python tigris), in the Museum of the Royal College 

 of Surgeons, measuring eleven feet in length, and having 291 vertebrae, the 253 

 following the axis support simple moveable pleurapophyses, articulated to concavo- 

 convex sessile diapophyses, and constitute the dorsal, abdominal, or trunk-vertebrae ; 

 70 of the anterior of these vertebrae have long hypapophyses, as in fig. 4, h, T. XIV, 

 they then begin to shorten, and subside to the ridge and tubercle, as shown in fig. 1 

 and 4, T. XIII, in the rest of the trunk-vertebrae. The first caudal vertebra has free 

 pleurapophyses, but they are short and bifurcate, the upper prong being the shortest ; 

 in the second caudal the left bifurcate rib is free, but the right is anchylosed to the 

 diapophyses ; the prongs are of equal length in this and the two following vertebrae. 



