i68 THE ARTISTIC ANATOMY OF ANIMALS 



Muscles of the Arm 



We should remember, at the outset, that in man the 

 muscles of the arm are divided into two groups : one 

 anterior, which contains the biceps, brachialis anticus, and 

 the coraco-brachialis ; the other, posterior, which is consti- 

 tuted by a single muscle, the triceps. 



In animals, we find them in the same number and arranged 

 in analogous fashion — that is to say, in two groups — with 

 respect to the bone of the arm. But then we find that they 

 have undergone a transformation with regard to their length, 

 and it is the change of general aspect which results from this 

 modification that we proceed to examine. 



We know that in quadrupeds, and especially in the 

 domestic animals, the humerus is relatively short in propor- 

 tion to the forearm. We have already seen, in dealing with 

 the bones, that whilst in the human species the humerus 

 is longer than the forearm, in the dog and cat these two 

 segments of the fore-limb are of equal length, and that the 

 humerus of the horse is, on the contrary, much shorter. 

 Now, let us suppose the human humerus to be shorter than 

 it is in reality ; the anterior muscles undergoing, very natur- 

 ally, the same reduction, will be uncovered only slightly by 

 those above — the deltoid and the great pectoral — or will 

 remain completely hidden by them. Thus would be found 

 realized the disposition which we meet with in quadrupeds 

 of the muscles of this region. 



With regard to the posterior muscular mass of the arm, it 

 does not undergo the same change. The muscle which 

 constitutes it — the triceps cubiti — occupies, on the con- 

 trary, a greater area. Let us suppose, further — for it is 

 the best method of comprehending the homologies which 

 now occupy our attention — the humerus of man to be 

 shortened as before, and directed downwards and backwards 

 (as in quadrupeds), this bone would form an acute angle 

 with the axillary border of the scapula. Let us suppose 

 also that the long portion of the triceps, instead of arising 

 solely from the superior part of this axillary border, is 

 attached to the whole length of the latter, and that the 



