e 'h 



164 ELEMENTARY ANATOMY, [LESS. 



ever, exceed that of all the rest of the limb put together, as 

 in the Apteryx. It may also exceed the length of the whole 

 body, as in the Pelican ; while a few Birds, e.g. the Martins, 

 have it remarkably short. 



In its being cylindrical in shape man's humerus is normal, 

 but it may be almost as broad as long, as in the Mole and 

 some Cetacea. The head of the hu- 

 merus is generally less spheroidal than 

 in man, with high projecting processes 

 (the tuberosities), as in the Carnivora, 

 e.g. the Dog. It may have the form of a 

 transversely extended articular ridge, as 

 in Birds. 



The shaft of the bone may be twisted 

 like the letter S, as in the Tortoises, but 

 FIG. 140. RIGHT Hu- that twist of the shaft which we find in 

 man is peculiar to him and to the high- 

 esl : A P es > though there is something like 



condyle; t\ capitel- it in Birds. 



lum. The greater (radial) and lesser (ulnar) 



tuberosities are very constant structures, 

 one or both appearing down to the lowest Batrachians. 



They may project much more than in man (as e.g., amongst 

 many others, in the Dog and Sheep), or the two maybe fused 

 into one, thus obliterating altogether the bicipital groove, as 

 is the case in the Cetacea ; or they may project much and 

 so sharply as to make that groove a very deep one, as in the 

 Turtle. 



The so-called " lesser " tuberosity may be as large as the 

 "greater" one, or even come to exceed it in size, as in the 

 Two-toed Sloth, the Bat Pteropus, and the Lizard Uromastix. 

 Beneath the lesser tuberosity a deep cavity may exist, as in 

 Birds : this is to allow air to enter the air-cavity within the 

 bone, many bones in many Birds being thus filled with air 

 instead of marrow. 



The rough surface for the deltoid is in man's humerus but 

 a faint indication of what may in other forms, e.g. the Seal, 

 Mole, Beaver, &c., be a very prominent ridge. 



The lower end of the bone may be either more expanded 

 relatively than in man, or less so. Thus, e.g., the condyles 

 may be very greatly produced, as in the Mole, Armadillos, 

 and Echidna, or they may be quite rudimentary, as in the 

 Deer and Hare. 



Very often a foramen may exist above the internal con- 



