THE ASTERIOR LIMBS. 



113 



the depressions above the inferior articular surface, poste- 

 riorly. 4. The level form of the facet articulating with the 

 OS magnum of the second row. 5. The presence of a small, 

 flat, vertical facet on the posterior contour of the upper 

 articular surface of the large metacarpal. 



In the Mule and Hinny, the small metacarpals are nearly 

 alike, as in the Horse ; the large metacarpal is flattened, as 

 in that animal, with marked depressions posteriorly. 



Fig. 71. 



Differential Characteks in the Metacarpus of other Animals. 



The number of metacarpal bones naturally varies with tbat of the 



digits : — 



In the Carnivora there are 5 



In tlie Pif? there are 4 



In Ruminants there are 2 or 3 



With rt-grard to their shape and form, they oflfer interesting differences, 

 whicli will now bo studied 



A. Ox, Sheep, Goat. — In these animals the metacarpal bones are 

 two in numl>er — a principal, which itself results from the consolidatioa 

 of the second and third metacarpals; another, altogether rudimentary, 

 situati d outwardly ; and a thinl — not constant — embedded in a fibroua 

 cord passing along the i-mer border of the principal metacarpal. 



The principal metacarpal is channeled ou its anterior face, and for 

 its wliole Itngtli, by a deep vascular fissure — a trace of the primitive 

 separation of the bone into two pieces. Tliis fi.ssure presents, inferiorly, 

 the anterior onfice of a canal that completely traverses the bone. The 

 posterior face is also marked by a very slight longitulinal groove. The 

 superior extremity exhibits, externally and pusteriorly, a single diar- 

 throflial facet for articulation with the rudimentary metacarpal. The 

 inferior extremity is divided by a deep notch into two articular surfaces, 

 which together resemble the single surface in the Horse; each articulates 

 with one of the digits ; the external is always smaller than the internal. 

 In the foetus, the two long bones that form the great metacarpal are 

 simply laid together, and their medullary canals are separated from 

 each otlver by tiie double partition which results from this apposition; 

 after their coalescence, however, the partitions are completely destroyed 

 by absorption, and in a short time there is only a single medullary canal 

 for the entire bone. 



The rndimentary metacarpal is only a small osseous stylet, articu- 

 lating, by a dial throdial facet, behind and to the outside of the superior 

 extremity of the principal metacarpal ; it is sometimes absent in the 

 Sheep and Goat. 



B. Camel. — The metacarpus of the Camel is very long, quadran- 

 gular in its up[>er two-thirds, and flattened behind and before in its 

 inferior third. Its posterior face is converted into a kind of concave 

 furrow, by the considerably raised borders of the bone. The superior 

 articular .surface is divided into two parts by a large roughened depres- 

 sion ; the inner part is on a higher level than the outer. The inferior 

 extremity is also divided into two articular surfaces by a very deep 

 notch ; each surface is condyloid in its anterior moiety, and is like 

 that of the Horse in its posterior moiety. 



C. Dog, Cat, Rabbit.— The five metacarpals of the Dog and Cat 

 articulate with each other, at their superior extremities, by lateral 

 facets; they offer, at their inferior extremity, a condyle prolonged back- 

 wards by an articular surface resembling that of the Horse. The 



4, 5, 6, first, second, and tbii'd booes of the upper row of the carpus; 7, 8, 

 of the lower row ; 9, rudimentary metacarpals; 10, principal metacarpal 

 12, internal digit. 



FOREARM and FOOT 



OF the ox (front 



view). 



1, Olecranon ; 2, body 



/of the ulna; 3. 



body of the radius; 



first and second bones 



11, external digit; 



