562 



MAMMALIAN ANATOMY 



class of bones appear to belong to animals of a finer breed, or to those 

 which have been better cared for. These are not sexual differences,, 

 nor are they dependent upon age. 



FIG. 435. 



HUMAN SKELETON IN THE POSTURE OF THE SKELETON OF THE CAT. 



HUMAN HUMERUS. 



The humerus is the longest bone in the human thoracic limb, hence 

 the arm is longer than the forearm ; in the cat the ulna is longer than 

 the humerus, hence the forearm is longer than the arm (Figs. 434,. 

 435). As compared with the cat's humerus, the human bone is more 

 slender and the extremities are more clearly defined from the shaft. 

 A constriction, the surgical neck, separates the shaft from the rounded 

 mass formed by the head and the two tuberosities. 



The head is a section of a sphere, and its smooth articular surface is 

 limited by a line which marks the anatomical neck. When the bone 

 is held with the internal epicondyle uppermost, the articular surface of 

 the head is also uppermost; when the cat's bone is so held, the articular 

 surface is at the side. In man the humerus hangs at right angles to the 

 scapula ; in the cat it is approximately in the same dorso- ventral plane. 



The greater tuberosity in the human humerus is more rounded 

 and less conspicuous than the corresponding prominence in the cat. 

 It is marked by three facets, for the insertion from above downward 

 of the supraspinatus, infraspinatus, and teres minor muscles. 



