1896.] MB. G. A. BOULBNBEE ON SCHLEGBL's GATIAL. 631 



hypapophyses on the cervical and anterior thoracic Tertebree are 

 less developed than in the other recent Crocodilians, and are not 

 directed forwards ; they are not developed beyond the eleventh 

 vertebra (twelth or thirteenth in the others). The chevron-bones 

 are all open dorsally. The first pair of ribs are inserted on the 

 sides of the proatlanto-atlantic hypapopbysis, or lower part of the 

 atlas-ring, and separated from each other at the base by a wide 

 interspace. The second rib differs from that of all Crocodilians I 

 have hitherto examined (including the Gavial, of which I have 

 examined the bone on a young specimen in spirit, and also the 

 atlas and axis preserved in the Museum of the Royal College of 

 Surgeons, — the Gavial-skeleton still being a desideratum in the 

 British Museum Collection), Osteolcemns excepted ; it is attached 

 to the centrum of the atlas (odontoid bone), near its suture with 

 the axis, by the capitulum only, the tuberculum being merely 

 indicated by a small upward process at a distance from the base 

 of the bone, and without any connection with the vertebrse. 



It is well known that in IchtJiyosaurvs the atlas bears a forked 

 rib, same as the axis and the other vertebrae behind it. It seems 

 that one Crocodilian at least presents an approximating feature. 

 The late Mr. Hulke has first pointed out in Metriorhynclnts (P. Z. S. 

 1888, p. 419) the presence on the " lateral pieces " (neurapophyses) 

 of the atlas of a tubercle situated in the level of the diapophysis on 

 the epistropheus, and he concludes that this tubercle should rank 

 as an upper atlantal transverse process or diapophysis. I have 

 been able to verify the correctness of this statement on several 

 well-preserved atlases of Iletriorhynchiis, still undescribed, from 

 the Leeds Collection, which my colleague Mr. Andrews has kindly 

 shown me in the Geological Department of the British Museum ; 

 and I quite agree with Hulke that " the position of this little 

 process in serial line with the upper transverse processes of the 

 other cervical vertebrse speaks distinctly in favour of its diapo- 

 physial character." We are, in consequence, justified in assuming 

 that, although, as we know from one specimen, the first rib is not 

 forked, it must have been connected with the diapophysis by 

 ligament, its head being attached to the side of the hypapopbysis 

 (" basilar piece ") of the atlas, or rather between the latter and the 

 centrum (odontoid bone) ; and such a condition may be regarded 

 as the most primitive known among Crocodilians, and as one from 

 which, as Hulke has shown, the abnormal position of the first rib 

 of recent forms may be derived and explained. 



The second rib in Metriorhynchus was attached by its capitulum 

 to the anterior border of the lower surface of the centrum of the 

 axis, or between the latter and the centrum of the atlas, and by its 

 tuberculum to a process (diapophysis) of the neurapophysis of the 

 axis. 



As regards recent Crocodilians, the information to be derived 

 from books appears contradictory, principally from the fact that 

 the various authors have dealt with different genera, and have in 

 some cases generalized their observations to the whole group. • 



