THE ANTEHIOB LIMBS. 



103 



Fig. 64. 



Laid on its posterior face, the liumerus of the Ass is in unsta})le equilibrium, if it 

 has to touch the plane by the epicondyle and epitrochlea ; this is not so with the 

 humerus of the Horse. If it is placed on its external side, the deltoid imprint 

 remains above the horizontal plane with the Ass, and touches it with the Horse. 

 Lastly, the epitrochlea descends nearly to the articular surface in the Ass, so that 

 the bone is almost in equilibrium when it is placed on its inferior extremity. 



The humerus of the Mule and Hinny resembles that of their parents, but 

 that of the Hinny is more like the Ass's, and that of the Mule the Horse's. 



Differential Characters in the Humercs of other Animals. 



Proportionately, the humerus is longer, and more inflected like an S, as the number of 

 apparent digits is increased. Therefore it is that, in the Carnivora, the characters of length 

 and inflection are most marked. 



A. Ox, Sheep, Goat. — In these animals, the furrow of torsion is less marked, and the 

 deltoid imprint less siilient than in the Horse, while 



the extremities are larger ind more curved. The 

 bicipital groove is divided into two depressions by 

 a median ridge ; tiie external trochanter is enormous, 

 and its very elevated summit is bent over the 

 bicii>ital groove. The head is better detached and 

 the trochlea deeper than in the Horse. The medul- 

 lary eanal of the humerus of the Ox is sometimes 

 cros-sed by an osseous band. 



B. Camel. — Humerus cylindrical and nearly 

 straight. Torsion furrow shallow ; nutrient foramen 

 on its anterior face. Bicipital groove doulde, the 

 inner cavity being larger than the external. The 

 inferior articular surface is relatively very narrow, 

 and tlie external trochlea deep. 



C. Pig. — The humerus of this animal is com- 

 pressed on both sides; the head is much bent back- 

 wards, which increases its 8 inflection. A single 

 bicipital groove placed within the superior extremity ; 

 the external trochanter voluminous, and the summit 

 turned over the bicipital groove. Deltoid imprint 

 and internal tuberosity of the body replaced by 

 simple muscular imprints. 



D. Dog and Cat. — The humerus is very elon- 

 gated and more S-curved than in all the other 

 animals, and the internal tuberosity is replaced by 

 some imprints ; while the bicipital groove is single, 

 and the nutrient foramen, on the posterior face, is as 

 in the Ox, Sheep, and Pig. Tlie coronoid fossa com- 

 municates with that of the olecranon by a foramen. 



E. Rabbit. — The humerus of this animal greatly 

 resembles that of the Dog, except that it is much 

 more flattened on each side, and the deltoid imprint 

 is on the anterior face and nutrient foramen on the 

 inner face of the bone. 



Forearm. 



This region has for its base two bones — the radius and cubitus (or i/luc), 

 united into a single piece {os antihrarhii) at an early period in most of the 

 domesticated animals. 



1. Radius (Figs. 65, 66). 

 This is a long bone, placed in a vertical direction between the humerus and 

 the first row of carpal bones, and divided into a body and two extremities. 



HUMERUS OF THE CAT AND RABBIT. 



, Humerus of tlie Kabbit. B, Humerus of 

 the Cat. 1, Condyle ; 2, trochlea ; 3, 

 diaphvsis ; 4, external trochanter ; 5, 

 internal trochanter ; 6, bicipital groove. 



