No. i.] INTERCALATION OF VERTEBRAE. 51 



PytJwn molnrns Linn. (P. tigris Daud). In a skeleton of this 

 snake in the Museum of the Royal College of Surgeons of Eng- 

 land in London, No. 602, the following peculiarities of structure 

 are to be seen. Up to the 14/th inclusive the vertebrae are 

 normal, each having a pair of transverse processes and a pair 

 of ribs. The next vertebra is normal anteriorly, and as far as 

 the level of the posterior surface of the transverse processes, 

 save that its neural spine is rather small from before backwards. 

 The transverse processes bear a pair of normal ribs. But 

 behind this pair of transverse processes the parts begin again, 

 rising again into a neural spine, and growing outwards into a 

 second pair of transverse processes, with a second pair of nor- 

 mal ribs. Posteriorly again the parts are normal. These 

 two segments are not the result of ankylosis, but of imperfect, 

 division. 



In the same specimen the i66th vertebra is normal on the 

 left side, bearing one transverse process and one rib, while on 

 the right side there are two complete transverse processes and 

 two ribs. The iS5th shows the same condition, being double 

 on the right side and single on the left. (Owen, 1853, p. 123; 

 Baur, 1889, p. 333; Bateson, 1894, pp. 103-105.) 



PytJion scbae (Gmelin), Museum Brussels. The I95th ver- 

 tebra is single on the right side, and double with two ribs on 

 the left. Besides 195 is ankylosed with 196. (Albrecht, 1883, 

 pp. 21-34, PL II, Figs. 1-4; Fiirbringer, 1888, vol. ii, pp. 975, 

 976 ; Baur, 1889, p. 332; Bateson, 1894, p. 105.) 



PytJion sp., Cambridge University Museum. i68th vertebra 

 double on the left side. (Bateson, 1894, p. 105.) 



Hydrns platnrus Linn. (Pclamis bicolor Daud), No. 763, 

 Yale University Museum. The 21 2th vertebra simple on the 

 left side, with one rib; double on the right side, with two ribs. 

 (Baur, 1889, P- 333-) 



Cimoliasaurus plicatus Phillips (Plesiosauria), No. 48,001, 

 British Museum, London. Cervical vertebra divided on one 

 side with two ribs. (Lydekker, 1889, p. 238; Baur, 1889, 

 p. 333; Bateson, 1894, p. 105.) 



In PytJion there may be as many as 435 vertebra, and in 

 Cimoliasaurus plicatus we have 44 cervicals. 



