Most of these peculiarities have reference to the place of origin of the artery, a subject already alluded to in the descriptions of the variations observed in the branches of the axillary and in the place of bifurcation of the brachial artery. In a considerable number of observations, the ulnar artery was found to deviate, in regard to its origin, in nearly the proportion of 1 in 13. In all cases but one, (in which it arose between two and three inches below the elbow-joint, in consequence of a late bifurcation of the brachial artery,) the place of origin of the ulnar artery was higher than usual. Moreover the brachial was, more frequently than the axillary, the source from which it sprang : indeed, the examples of its origin from the trunk at different parts appeared to decrease in number upwards.
The position of the ulnar artery in the fore-arm is more frequently altered than that of the radial. When it arises in the usual way, the course of this artery is not often changed ; but it has been seen to descend apart from the tendon of the flexor carpi ulnaris, instead of being close to its radial border.
The position of the ulnar artery in the upper arm, when it arises high up, has been previously adverted to. In the fore-arm, it almost invariably, in cases of premature origin, descends over the muscles arising from the inner condyle of the humerus, only one exception to this rule having been met with. Most commonly it is covered by the fascia of the fore-arm ; but now and then a case occurs in which the vessel rests on the fascia, and is subcutaneous. In a very few instances the artery lay partly beneath the skin, and partly beneath the fascia, being subcutaneous for a short distance in the upper part of the fore-arm, and subaponeurotic lower down.
As to size, the ulnar artery presents some peculiarities, which, being accompanied by deviations of an opposite and compensating character in the radial artery, will be noticed with that vessel.
From Quain's Anatomy.