470 



Prof. W. K. Parker. 



[Mar. 22, 



more common kind of articulation in Archaic Reptiles, whilst the 

 " proccelous " mode is almost universal in the existing Reptiles. 



But, in fact, Birds are very eclectic in the manner in which their 

 vertebral centra a,re articulated, and any kind of articulation that 

 happens to be the best for the particular region in which it is found 

 is selected, so to speak. 



I will show, 1st, in what families the dorsal vertebrae are opistho- 

 ccelous ; 2ndly, the modification in Birds of that type of articulation • 

 and then how many sorts of articulation they exhibit in this or that 

 Family. 



In his valuable memoir on the Penguins,* the late Professor 

 Morrison Watson greatly understates the number of Families that 

 have this peculiarity, namely, the Penguins and the Auks. Now 

 amongst the Steganopods or Pelicanine types they are found in the 

 Cormorants and Darters (Flatus). 



Amongst the Old World Pygopods this structure occurs in all the 

 Alcidse — Alca, Uria, Ciceronia, &c, and in all the Charadriomorphse 

 or Shore birds (Limicolas), and in the Gulls (Laridae, Lestridae, &c), 

 but not in the Petrel tribe — Procellaridae. 



But amongst the most highly specialised arboreal " Altrices " I 

 have long been familiar with this peculiarity in the great Parrot 

 Family — Psittacidae — in which, strangely enough, it is combined with 

 a very unlooked for character, namely, with terminal epiphyses — a 

 structure which begins to show itself in the Ornithorhynchus, in the 

 caudal region. 



This is very remarkable in these high, hot-blooded birds, for in the 

 whole class epiphyses are very rare, only, one being constant ; this is 

 found in the cnemial crest of the tibia. 



But the Parrots are not the only high kinds of birds in which the 

 dorsal vertebras are opisthocoelous ; I have within the last two years 

 found it in that remarkable type, the Oil Bird (Steatornis caripensis), 

 an archaic, frugivorous Goat-sucker — a bird which has no near allies, a 

 crepuscular Cave-dweller, found only in Cumana and a neighbouring 

 island, and manifestly a waif from a nearly lost group. 



On the Modification of the Opisthocoelian Articulation in Birds. 



The cup and ball in these opisthocoelous dorsals of birds is very 

 different from what is found in the proccelous vertebrae of the 

 Ophidia ; in them it is fairly circular or hemispherical, whilst in 

 birds it is generally scarcely more than three-fifths of an ellipse, and 

 the upper margin is emarginate, having a concave outline answering 

 to the general concavity of the floor of the spinal canal. 



That which shows such intense specialisation in the proccelous 

 vertebrae of the Serpents is the remarkable manner in which an 



# " Challenger" Eeports, Zoology, vol. 7, p. 16. 



