212 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 20, 



prominence, as in the Swan. The inner border of the canal above 

 the bridge is more defined than in the Swan. 



In the Falkland Island Goose, the tendinal canal is more oblique 

 and its lower outlet more to the inner side than in the Common 

 Goose. 



In the Pelican {Pelecanus onocrotalus)^ the lower end of the tibia 

 is less expanded than in the AnatidcE and most extinct birds : the 

 breadth and depth are equal. The intercondyloid space is wider than 

 either condyle, which are alike. The bridge is median, but narrow 

 and oblique ; spanning a wide and deep canal, the lower outlet of 

 which looks forward, opening immediately above the intercondyloid 

 space. The posterior trochlear surface is nearly flat transversely, 

 and has a low and broad median rising. 



The Great Gull (Larus marinus), with the breadth and depth of 

 the expanded lower end of the tibia equal, has a wide intercondyloid 

 space ; the inner condyle is more prominent, and is shorter than the 

 outer one : the posterior trochlear surface is concave across. The 

 bridge is submedian, narrow, descending rather obliquely from the 

 inner to the outer side ; spanning a wide canal, with the lower outlet 

 above the intercondyloid space, and separated from it by a feeble 

 narrow ridge. The canal leading to the bridge is broad, and is 

 bounded on each side by a short sharp ridge. 



In the Albatros {Diomedea exulans, fig. 14), the breadth, depth, 

 and prominence of the condyles are equal ; but neither of them is 

 so broad as the intercondyloid space. The bridge is submedian, 

 transverse, broad, with the lower outlet of the wide canal transversely 

 elliptical and large, looking directly forwards, just above the inner 

 half of the intercondyloid space, and situated relatively lower down 

 than in the Swan. The trochlear articular surface is not produced 

 forwards in advance of the intercondyloid space, nor does that space 

 show any fossa or depression. 



In the Alca torda, the breadth a little exceeds the depth of the 

 condyles. These are subequal, with a wide intercondyloid space : the 

 posterior trochlear surface is very slightly concave across, and with a 

 feeble median rising. The bridge is submedian and broad : the 

 inner ridge of the canal leading to it is most developed, the lower 

 outlet is transversely elliptical and just above the intercondyloid 

 space. The ectocondyloid surface is flat : the entocondyloid one is 

 subconcave, with a median tubercle. 



In the Grebe {Colymhus glacialis) — so remarkable for the modi- 

 fication of the proximal end of the tibia, — the distal end of the bone 

 deviates little from the usual natatory type. The wide intercondy- 

 loid space is deeper, the narrow convex condyles being more pro- 

 duced than in the Albatros and AnatidcB. The posterior trochlear 

 surface has a well-marked outer ridge, and a feeble median rising. 

 The bridge is median, transverse, very narrow in the middle, spanning 

 a very deep and wide canal, the large lower aperture of which looks 

 directly forwards, opens just above the intercondyloid space, and has 

 a thin sharp lower transverse border. The canal leading to the 

 bridge occupies almost the whole of the breadth of the bone. 



