424 MR. J. W. HULKE ON THE SKELETAL [NoT. 20, 



arch (the expanded root of which, descending laterally on the noto- 

 chordal sheath, represents a pleuroceutrum), and of an inferior or 

 ventral ossicle lying vertically beneath it, and so representing 

 Gaudry's hypocentrum, there are also present distinct inferior ossicles 

 in thenotochordal sheath, intercalated one between each pair of com- 

 posite vertebral bodies, and thus intruded between the hypocentra. 

 Similarly su[)erior intercalaries occur between the neural arches. To 

 such inferior " intercalaria " the term intercentra is strictly pertinent. 



In the Ganoid Amia calva the cartilaginous tips of the trans- 

 verse processes are structures having some correspondence to ribs. 

 Now Dr. G. Baur mentions that in Amia calva the lateral (or trans- 

 verse) process (Basalstumpf, Gotte) at a certain point in the vertebral 

 column, near the end of the body-cavity, passes from the centrum 

 of a vertebra to the intercentrum next immediately following (30). 

 In the only skeleton of Amia calva accessible to me (one prepared 

 by Hyrtl preserved in the Museum of the Royal College of Surgeons), 

 I find that behind the 6th vertebra following the body-cavity arch- 

 less and arch-bearing centra alternate regularly ; and, except for a 

 slight difference of size, these two kinds of centra are barely distin- 

 guishable. The lateral or transverse process, which in that part of 

 the vertebral column which corresponds to the body-cavity is borne 

 by the arched centra, alone present there, is not, in this skeleton, in 

 the region behind tlie body-cavity transferred from the arch-bearing 

 to the here intercalated archless centra (or intercentra) ; but the 

 transverse process continues to occur only on the arch-bearing centra, 

 until at the caudal end of the column, through reduction of bulk 

 and through crowding, the distinctness of the com])onent pieces of 

 the column is lost. 



Ascending in the vertebrate scale, Hatteria, as shown by Dr. G. 

 Baur, I'urnishes in its anterior vertebrae an example of the connection 

 of a rib with a true intercentrum Here tiie capitulum of the 

 furcate rib, mostly represented by ligament, is ligamentously con- 

 nected with the intercentrum, whilst the tuberculura rests on the 

 centrum. I find this arrangement present in the three anterior 

 pairs of ribs in two skeletons of Hatteria now before me. The 

 secondary connection of the ribs with the permanent vertebrse, and 

 the arrangement in Hatteria demonstrating the connection of the 

 capitulum costce and the intercentrum, would seem to favour the 

 idea that the Crocodilian basilar piece is morphologically an inter- 

 centrum. The body of evidence, however, is I think, unfavourable 

 to this conception ; and this, together with the fact that in the early 

 embryo the basilar piece is continuous with the pars odontoidea and 

 with the neurapophysis (including the hemicentroids, Albrecht), 

 gives very great probability to the hypothesis that the basilar piece 

 is really that which R. Owen termed it — the inferior part of the 

 centrum of the atlas. This is also C. K. Hoffmann's view of it (31). 



The morphological equivalence of the Crocodilian basilar piece to 

 the foremost of the subvertebral wedge-bones in Ichthyosaurus does 

 not seem to me proven, but rather the contrary. Probably in the 

 Enaliosaur the " body " of the atlas is the equivalent of the Croco- 



