I860.] OWEN VERTEBRA FROM FROME. 



495 



the structure of their scapulo-coracoid arch so significant a departure 

 from the Mammalian rule, and so close a resemblance to certain Se- 

 condary Reptiles. The vertebral modifications, in the Orniihorhyn- 

 chus and Echidna, to which I allude, are the " slight concavity of 

 the terminal articular surfaces " and a construction of the uniting 

 soft parts which I discovered in 1840, and which is described and 

 figured in the article " Monotremata," in the ' Cyclopaedia of Ana- 

 tomy,' vol. iii. (1841) p. 375, fig. 174. The structure is as follows : 

 — " The articular surfaces of the vertebrae, which are slightly con- 

 cave, are joined together by a thick circular band of ligamentous 

 fibres, attached to the circumference of the articular surface, en- 

 closing a central oblate spheroidal cavity, lined by a synovial mem- 

 brane and filled with fluid." 



Now, if one should look on the figure of the section of the ver- 

 tebrae there given, he will see that, were ossification to extend into 

 the fibrous basis of the synovial cup, the biconcave or amphicoelian 

 type of vertebra would be established. 



But it may be objected, in regard to another character of the little 

 fossil vertebrae, that they show a mode of rib -articulation agreeing 

 with the Saurian and not the Mammalian type. In Mammals, as a 

 rule, the free rib, which has both head and tubercle, joins by the 

 former to an articular surface common to two centrums and their 

 intervertebral ligament. In those rare abnormal cases, however, 

 where the ribs of the last cervical vertebrae have not coalesced as 

 usual, but show an abnormal size as well as freedom, they articulate 

 by both parts of the bifurcate end to the same vertebra; and here, 

 again, the Monotremes come to our aid in an approximative appre- 

 ciation of the nature of the triassic vertebrae in question. The ribs 

 of the neck remain longer unanchylosed in the Monotremes than in 

 other Mammals. In a young but nearly full-grown Echidna I found 

 them, as regards bony union, " detached from all the cervical ver- 

 tebrae except the atlas. The vertebral end of the cervical rib is bi- 

 furcated ; the lower branch, representing the head, is articulated to 

 the transverse process or tubercle [parapophysis] developed from the 

 body of the vertebra ; the upper branch, representing the costal 

 tubercle, is articulated to a transverse process [diapophysis] developed 

 from the side of the base of the neural arch " (vol. cit. p. 375). 

 Such a condition of rib-articulation agrees with that indicated by the 

 structure above described in the first and most perfect of the little 

 vertebrae discovered by Mr. Moore. 



Although the neural canal is relatively more capacious in the small 

 Lizards than in Crocodiles, I have met with no cold-blooded air- 

 breathing animal with anchylosed neural arch offering so large a 

 proportionate size of the canal as in the fossil vertebrae in question. 

 Had I known only this character of those vertebrae I shoidd have 

 suspected their being Mammalian, that character having served to 

 distinguish between fragmentary specimens of large Saurian and Ce- 

 tacean fossil vertebrae. 



The anchylosis of the neural arch to the centrum is as common, 

 almost, in recent Lizards as in Mammals. The vertebrae transmitted 



