221 



1145. The skull of the Crested Penguin (Aptenodyttt (Ewlypffs) cArytocome). 



Prctcnted by W. Bullock, 



Genus Alca. 

 \ 140. The skeleton of the Razor-billed Auk (Alca torda). 



The exterior surfkcr of the cranium if deeply excavated by the fuperorbiul glandular (owe 

 and by the temporal and occipital depressions. There are 21 free vertebra between the skull 

 and sacrum, of which the last nine support moveable ribs, the first two sacral vertebrae having 

 each a similar pair of long and slender ribs, extending to near the end of the tail. All tin- 

 ribs, save the first two pairs, have bony hnmapophyses, which progressively elongate, and, 

 with the exception of the last pair, directly articulate with the sternum. This unusual ex- 

 tension of osseous hoops about the parietes of the abdomen relates to the power of compress- 

 ing the abdominal air-cells during submersion in these diving birds. There are 9 caudal ver- 

 tebra*. The hypapophyses are unusually developed in the dorsal region. 



Mu*. South. 



1 147. The skull of the Razor-billed Auk (Alca torda), with the horny sheath of the 

 bill preserved. MM. Brit. 



1148. The dried head of a Razor-billed Auk (Alca torda). 



Prenentcd by W. Bullock, K*q. 



1 149. The dried head of the Little Auk (Alca alle). Pretexted by W. Bullock ; t*q. 



1150. The mutilated skull of the Great Auk (Alca impennit), with the dried integu- 

 ments, and the horny sheath of the bill. MM. Brit. 



1151. The skull of the Great Auk (Alca impennu). 



The superorbital glandular impressions meet along the interorbital space, and the tem- 

 poral depressions above the parietal region ; these depressions are then continued forward*, 

 at a right angle with the parietal part, to the postfrontal processes. 



Htmterian. 



1152. The right tympanic bone of the Great Auk (Alca impenniif). Ifuntfrian. 



1153. Nine dorsal vertebra*, with their pleurapophyses, of the Great Auk (Alca im- 

 petmu). In these the remarkable development and modifications of the hyp- 

 apophyscs, and the bone-tendons developed in the muscles of the back, are 

 shown. IfuHtrna*. 



