530 
BE. A. GUNTHER’S DESCRIPTION OF CERATODUS. 
singular fact, the gradual change of insertion of the following ribs, first, to the bottom 
of the neurapophysis, then to the centre of the axis, and finally to the parapophysis, 
shows clearly that this bone is a rib. Nor is the application of parapophysial elements 
of the first vertebra, for support of the scapular arch, of very rare occurrence in fishes ; 
it is observed in Bagrus and other Siluroids. 
The haemal pieces of the tail (Plate XXX. fig. 2, and Plate XXXVIII. figs. 7-9) are 
built up similarly as the corresponding dorsal parts. We have again 
a. A cartilaginous portion of the heemapophysis (c 2 ), supplemented by 
h. A haemal spine (/), with its proximal end osseous and forked to form a canal for 
blood-vessels (k), but without a trace of a ligamentum longitudinale inferius. 
c. Interhsemal first (to). 
d. Interhsemal second ( n ). 
These pieces remain distinct very nearly to the end of the tail ; but all become gra- 
dually weaker and shorter, and also ossification ceases in some of the posterior ones. 
Finally the number is reduced by the coalescence of the haemal spine with the haem- 
apophysis, and the pieces near to the extremity of the tail are quite rudimentary and 
scarcely distinguishable. 
Small and short dermo-neurals (Plate XXX. fig. 2, and Plate XXXVIII. figs. 4 & 5 . . .) 
may be distinguished from the interneural of the seventeenth segment; they gradually 
increase in length towards the middle of the tail, where they are very long ; they are all 
obliquely directed backwards, assuming a more horizontal direction the nearer they are 
to the end of the tail. They are exceedingly numerous, four or five or more corresponding 
to a single vertebral segment — and form a double series, one series on each side of the 
fin. This peculiarity, which Ceratodus has in common with Lepidosiren , reminds us of 
those fin-rays of Teleosteous fishes which can be more or less completely split into a 
right and a left half. The dermo-neurals of Ceratodus are not articulated to the extre- 
mities of the interneurals, but overlap them for a considerable distance of their length. 
The shape and arrangement of the dermo-hsemals is exactly^ the same as that of the 
dermo-neurals. No ossification takes place in either of them ; they consist entirely of 
cartilage, in which numerous spindle-shaped cells are imbedded, many of these cells 
being produced at both ends into a very long process (Plate XXXVI. fig. 7). 
The Scapular Arch (Plate XXX. fig. 2, Plate XXXV. fig. 1, Plate XXXVI. figs. 2 & 3). 
The scapular arch of Ceratodus is, with regard to the persistence of the primary carti- 
laginous condition and to the development of superficial bones, extremely similar to that 
of Lepidosiren* . The primordial cartilaginous arch consists of three pieces, viz. a single 
* Professor Owen was the first who, from the examination of a small example (far from being “ half-grown”), 
pointed out the primordial condition of the scapular arch in Protopterus, whilst Professor Peters was enabled to 
supplement the account of his predecessor from the examination of fresh specimens. Recently the shoulder- 
girdle of this fish has been made the subject of special research by Professor Gegenbattr and Mr. Parker; and 
it is singular that these two anatomists prefer to criticise the almost unavoidably imperfect first account, instead 
of availing themselves of the researches of the second of their predecessors. 
