OF THE GREAT AUK, OR GARFOWL. 333 



The sternum, perhaps the most characteristic of natural affinity of any single bone in 

 the bird's skeleton, exemplifies the essential distinction of the two species, which are 

 alike adaptively modified for marine existence, with abrogation of the power of flight. 



In the Penguin the sternum is destitute of episternal process, and has two posterior 

 notches, equalling in depth half the length of the entire bone. The front and lower 

 borders of the keel are straight. The coracoid grooves meet at the mid liue, and their 

 posterior wall is developed into a broad triangular process, with an obtuse apex, the 

 outer angle of the base of which answers to the costal process of the sternum in Alca 

 impennis. The costal part of the lateral border is relatively shorter in the Penguin, and 

 affords articulation to only six hsemapophyses. The lateral margins behind the costal 

 portion converge to the posterior part of the sternum, the middle part of which between 

 the lateral styles narrows to a point where the keel ends. 



The coracoids in Aptenodytes are conspicuous for their great length and strength, for 

 their columnar-like convexity transversely on the outer or fore surface, and their 

 flattened hinder or inner surface, which is concave transversely at its lower third. In 

 Aptenodytes antarcticus the length of the coracoid is four-fifths that of the sternum ; 

 in Alca impennis it is less than two-fifths. The inner lamelliform process from the 

 scapular end is more produced in Aptenodytes, and is notched in Eudyptes, instead of 

 being perforated ; the outer lamelliform process from the sternal end is much less pro- 

 duced. The scapula in Aptenodytes is remarkable for its unusual breadth as compared 

 with that of other birds ; it is nearly twice as long as the humerus, whereas in Alca 

 impennis it is shorter than the humerus. 



The clavicles in the Penguin are also of unusual breadth towards their upper ends, 

 and converge to their medial union at a more acute angle than in Alca impennis. The 

 humerus, besides being relatively shorter in the Penguin, is broader and more compressed, 

 less expanded at both ends, but especially proximally. 



The pneumatic fossa is much deeper, but does not extend into the shaft ; the two 

 olecranial grooves are relatively narrower, and restricted to the posterior inferior angle 

 of the lamelliform shaft ; a sesamoid in the extensor tendon plays upon each. The 

 articular surfaces for the radius and ulna are feeble convexities upon almost the same 

 transverse line, and the joint scarcely allows of the movements of flexion and extension. 

 In the Alca impennis it is adapted for much freer motions. 



musculi recti capitis antici : these pits are bounded externally by strong ridges descending and diverging from 

 the sides of the occipital condyle to the hypapophysial tuberosities. From the outside of the base of each 

 tuberosity a buttress flies upward and outward to the paroccipital, circumscribing the space in which lie the 

 carotid and pneumogastric foramina. The pretympanic fossa between the alisphenoid and mastoid rises verti- 

 cally for more than half an inch ; its inferior subcircular opening or entry is 4 liues in diameter. There are no 

 pterapophyses. The coalesced palatines present a narrow, oblong, flattened surface below ; and from the mid line 

 of the posterior part descends a triangular crest of bone, between the pterygoid articulations. The palatal 

 nostril is single, medial, 2 lines wide by 8 lines long. 



