1899.] OSTEOLOGY OF THE PYQOPODES. 1035 



It is probable that the long styloid free rib of the last cervical 

 or cervico-thoracic vertebra was originally larger and connected 

 with the sternum by means of a sterual rib ; in other words, this 

 represents a thoracic vertebra which has been transferred to the 

 cervical series by the loss of the sternal segments and its ribs. 

 Thus, what is now the first was earlier the second thoracic 

 vertebra and rib. 



In the Podicipides this transference of vertebra from the thoracic 

 to the cervical series is still more marked, inasmuch as what now 

 forms the first thoracic vertebra and rib in the Diver is in the 

 Grrebe the last cervical. This seems the most satisfactory way of 

 explaining the presence of the long free ribs in both Diver and 

 Grebe, and wherever else they occur. The transference of the 

 2nd pair in the Grebe seems to have been comparatively recent, 

 inasmuch as the uncinate is still retained. 



If this interpretation be correct, and it is one which was, I beheve, 

 originally put forward by the late Prof. T. J. Parker, then one more 

 thoracic segment is represented in the Grebe than in the Diver, 

 inasmuch as what now answers to the 1st thoracic of the Grebe 

 really represents the 3rd, and what now answers to the 6th — the 

 last vertebra now connected with the sternum by a sternal rib — 

 represents the 8th thoracic vertebra. The 6th and 7th vertebrae 

 have already fused with the synsacrum. The 7th ( = 9th) ceases 

 to be connected with the sternum, and the rib of the 8th ( = 10th) 

 vertebra is represented only by its sternal segment. In the Diver 

 there is only evidence for 9 thoracic vertebrae, the 9th now venturing 

 but a minute stvlet partly fused with the preacetabular ilium, and 

 projecting from its ventral border as a small spine. 



The presence of these free ribs is exceedingly interesting, they 

 form one of the many links in the chain of evidence, hinted at by 

 Mr. Beddard (1), which goes to show that a shortening of the 

 sternum has taken place. 



The ribs and uncinate in both Grebes and Divers are relatively 

 broad and flat and of moderate length. In all these particulars 

 they differ markedly from the Alcidse, to which the Pygopodes bear 

 a superficial resemblance. In this last group the sternal and 

 thoracic ribs are of great length. Especially is this the case with 

 the hindmost ribs, wliich are of enormous length, extending 

 backwards so as to project beyond the level of the free end of 

 the pubes. 



vi. The Sternum ai^d Pectokal Girdle. 



The sternum of the Colymbi is very long and bears a superficial 

 resemblance to that of some Alcidae. It can be immediately 

 distinguished therefrom amongst other things by the shallower 

 carina, the feebly developed spina externa, and the large lingui- 

 form metasternum, whicii projects considerably beyond the posterior 

 lateral processes. 



The sternum of the Podicipides differs very markedly from that 

 of the Colymbi. In the first place, it is conspicuously shorter. In 



