xv.] CETACEA. 277 



In Hyrax the humerus is straight, with a very prominent 

 outer tuberosity, moderate deltoid ridge, rather compressed 

 inferior extremity, large supratrochlear, but no supracon- 

 dylar, perforation. The ulna and radius are complete and 

 subequal, often ankylosing together in old animals. 



In the CETACEA, the bones of the arm and fore-arm are 

 usually very short, broad, and simple in their characters 

 (see Fig. 103). The humerus has a large globular head, 

 which moves freely in the glenoid cavity of the scapula, 

 the tuberosities are fused into one, the bicipital groove 

 being absent ; the lower end is broad and flattened, and 

 its inferior surface is divided into two nearly equal flat 

 surfaces placed side by side (one external, the other internal), 

 and meeting at a very obtuse angle. The equally flat 

 upper surfaces of the radius and ulna are applied to these, 

 and so united that scarcely any motion is permitted between 

 them, and often in old animals ankylosis takes place at 

 the joint. 



The ulna and radius are parallel to each other without 

 any indication of crossing : the former has a tolerably well- 

 developed olecranon process projecting directly outwards 

 from the shaft of the bone ; the radius is extremely simple 

 in form, wider distally than proximally. 



In the Rorquals (Balanoptera and Megaptera) these bones 

 are considerably elongated. 



In the SIRENIA the bones of the fore-limb are formed on 

 a different type, as there is a distinct, though small and 

 simple, trochlear articulation at the elbow-joint. In the 

 Dugong, the humerus is small in the middle of the shaft, 

 and expanded at each end. The tuberosities are very pro- 

 minent, especially the outer one, and the bicipital groove is 

 distinct. The internal condyle is prominent, the anconeal 

 fossa small, and there is no supracondylar perforation. In 



