OSSEOUS SYSTEM. 13 



animals it is very short, as in the true Cetacea, and in many of the 

 digging and aquatic Mammalia. On this account it frequently 

 obtains quite a peculiar breadth, being provided with singular pro- 

 cesses or inequalities of surface for the attachment of muscles, as 

 in the Mole and Monotremata. It is on the other hand longest and 

 thinnest in the Cheiroptera, and in all the Apes, especially the Gib- 

 bons, Orang-utang, &c. It is much longer in the very anthropoid 

 Chimpanzee, than in Man. The inferior articulating extremity is 

 formed into one or two pulley-like surfaces for connexion with the 

 bones of the fore-arm. The olecranal fossa is perforated in differ- 

 ent Apes, Carnivora, and Rodentia. There occurs also frequently 

 in these orders, as also in many Edentata and Marsupiata, an open- 

 ing in the internal condyle for the passage of the median nerve and 

 brachial artery. The structure of the scapular and humeral bones 

 in the Monotremata Ornithorynchus, and Echidna, is of a very 

 opposite character, the scapular arch in them being arranged ac- 

 cording to the type of the Saurians. The scapula is long and sabre- 

 shaped, and, with a peculiar piece situated more inferiorly, and 

 connected with the sternum, which corresponds completely with the 

 coraco-clavicular bone in Birds, forms an articulating cavity for the 

 humerus. The thin anterior clavicle, corresponding to the furcular 

 bone, unites with that of the opposite side, and is firmly supported 

 by the anterior border of the T-shaped manubrium sterni. Beside 

 these, there lies upon each side a peculiar quadrangular bone be- 

 tween the manubrium and the coracoid, which reminds us of a sim- 

 ilar structure in the Lizards. 



Still greater differences are met with in the bones of the Fore- 

 arm and Hand, especially the latter. The element in which the 

 animals live, whether air or water, upon or beneath the surface 

 of the earth, has a special influence upon these parts, which are 

 further modified by particular wants and modes of existence. 

 In general, we find two bones in the fore-arm, which admit of a 

 greater degree of rotation in the Quadrumana, the Carnivora, and 

 Marsupiata, than in the remaining classes. This motion is however 

 less even in the higher Apes, than in Man, and pronation and su- 

 pination are much more limited. The ulna is constantly longer than 

 the radius, and provided with an olecranon of variable size, which 

 is all but absent in the true Cetacea, where the two short bones 

 of the fore-arm lie immovably behind each other, and are very 

 flat like the whole extremity, which is constructed after the fashion 

 of a fin. Even in the Rodentia and Insectivora, the radius which 



