ORIGIN OF MAMMALS 



552 UKlLrllN Ul" 1V1A1V11V1AI^» XIX. 9 



The vertebrae are very reptile-like, especially the cervicals, which 

 bear separate ribs, as in the synapsid reptiles. There are seven cervical 

 vertebrae, but in the dorsal region differentiation has proceeded less 

 far than in other mammals, there being 16 ribs in the spiny ant-eaters 



Fig. 327. Skull and skeleton of a female platypus. 



at. atlas; c. coracoid; cl. clavicle; ep. epipubic bone; /. femur; fib. fibula; 

 h. humerus; id. interclavicle; is. ischium; j. jugal; m. maxilla; pc. precora- 

 coid; pm. premaxilla; pub. pubis; pv. prevomer; r. radius; sc. scapula; st. 

 sternum; sq. squamosal; t. tooth; ti. tibia; u. ulna. (Modified after Owen.) 



and 17 in the platypus, with 3 or 4 lumbars in the former and only 2 

 in the latter. The ribs articulate only with the bodies of the vertebrae, 

 not with the transverse processes. The tail is vestigial in Zaglossus, 

 but forms a flattened swimming-organ in the platypus. The limbs and 

 their muscles and girdles are remarkably reptilian (Fig. 327). They 

 tend to be held laterally rather than beneath the body and in general 

 the ventral parts are far better developed than in modern mammals, 

 and this is sometimes spoken of as a 'plate-like' condition. In the 

 pectoral girdle there are separate clavicles and a median interclavicle. 

 The coracoid region includes two quite large and separate bones, the 



