THE ANTERIOR 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. 



Differential Characters in the Metacarpus of other Animals. 



The number of metacarpal bones naturally varies with tliat of the 



digits : — 



In the Carnivora there are 5 



In the Pig there are 4 



In Ruminants there are 2 or 3 



With regard to their shape and form, they offer interesting differences, 



which will now be studied. 



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

 two in number — a principal, which itself results from the consolidation 

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

 situated outwardly; and a third— not constant — embedded in a fibrous 

 cord passing along the inner border of tlie principal metacarpal. 



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

 its whole length, by a deep vascular fissure — a trace of the primitive 

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

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

 posterior face is nlso marked by a very slight longitudinnl groove. The 

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

 throdial 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 other by the 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. 



Tiie rudimentary metacarpal is only a small osseous stylet, articu- 

 lating, by a diarthrodial facet, beiiind 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 upper 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 

 extn mity 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 



forearm and foot 



OF THE ox (front 



view). 



1, Olecranon ; 2, body 



of the ulna ; 3, 



body of the radius; 



first and second bones 



rudimentary metacarpals; 10, principal inetacarpals ; 11, external digit; 



4, 5, 6, first, second, and third bones of the upper row of the carpus; 7, 



of the lower row ; " " ' ' 



12, internal digit. 



