AlcIDJS,] OSTEOLOGIA AVIUM. [ALCINJE. 



Alca, Linn. 



Impensis, Linn. 



The skeleton of this bird has been lately fully described in the transactions of the 

 Zoological Society. The paper was read June 14th, 1864, by Professor Owen, 



Alca, Linn. 



Torda, Linn. 



Cranium very similar in shape to that of the foregoing. 



Sternum also similar, but furnished on each side with lateral fissures ; post orbital 

 process pointing downwards. 



Pelvis also similar. 



Wing-bones slightly flattened, but not so much so as in .4. impensis. Metatarsal 

 bones anchylosed together. 



Remaining bones very similar. 



Fratercula, Briss. 



Arctica, Linn. 



Cranium in some respects similar to the genus Alca. The space between the upper 

 part of the orbits very narrow, the orbital septum almost entirely wanting; orbits very 

 large, thus allowing a very small cavity for the brain ; the post orbital process very 

 long, and pointing upwards. 



Sternum with a slight foramen on each side of the keel, near the hinder margin, the 

 xiphisternal portion extending far backwards ; keel deep, much excavated in front, and 

 arched on its lower edge. 



Pelvis very similar to Alca torda. 

 , Wing-bones slightly flattened. 



Leg-bones. Metatarsus with a slight groove down the front. 



Measurements. 



Tenths. 



Length of humerus ..... 22 



Length of ulna 20 



Length of metacarpus 15 



Length of femur 12 



Length of tibia 23 



Length of metatarsus 10 



Length of sternum 31 



Tenths. 



Breadth of posterior margin of sternum 14 

 Breadth of anterior margin of sternum 9 



Depth of keel 9 



Length of head 29 



Breadth of head 11 



Length of pelvis 30 



Breadth of pelvis 11 



215 



