32 THE ARTISTIC ANATOMY OF ANIMALS 



median nerve, or in case of a premature division of this 

 artery to the ulnar branch of the same.* 



There is also found in some mammals a perforation of 

 the thin plate of bone which, in others, separates the ole- 

 cranon fossa from the coronoid. This perforation is some- 

 times found as an abnormality in the human humerus. 



As does the sternum and the skeleton of the shoulder, the 

 humerus of birds presents differences correlated to the 

 functions which the thoracic limbs are destined to fulfil. 

 Lying on the side of the thorax, directed obliquely down- 

 wards and backwards (Fig. 21), it is proportionately longer 

 in individuals of powerful flight than in those which fly 

 less or not at all. In the vulture it projects beyond the 

 posterior part of the pelvis ; in the cock it does not even 

 reach the anterior border of the same. To these differences 

 in length are added differences in volume and in the develop- 

 ment of the processes which serve for muscular attach- 

 ment, which are more considerable in birds of powerful flight. 



The humerus is so placed that the radial border, external 

 in man and quadrupeds, looks upwards, with the result that 

 the surface of the bone of the arm, which in these latter is 

 anterior, in the former looks outwards. The humeral head, 

 which is turned forwards and a little inwards, is convex 

 and elongated in the vertical direction. Behind and above 

 this head is found a crest for the insertion of muscles. It is 

 the same for the region below, where there is a tuberosity 

 whose inferior surface presents a pretty large opening 

 which looks inwards to a fossa from the floor of which a 

 number of minute openings communicate with the interior 

 of the bone. This is the pneumatic foramen of the humerus. 



It is of interest to remember in connection with this subject 

 that in birds, in keeping with the conditions of flight, every 

 system of organs is adapted to diminish the weight of the 

 body. We particularly draw attention to the osseous 

 framework, the structure of which is such that the weight 



* For further details of this anomaly, see Testut, ' The Epitrochlear 

 Process in Man ' (International Journal of Anatomy and Physiology, 1889) ; 

 A. Nicolas, ' New Studies on the Supratrochlear Process in Man ' (Review 

 of Biology of tlie North of France, t. iii., 1890-18Q1). 



