108 SKULL- OF ECHIDNA CHAP. 
affairs. It must be remembered, however, that the Cetacea 
show the same characters, though it is possible that they too 
are developed from a low mammalian stock. In the vertebral 
column we find the typical mammalian seven cervicals; but 
those characteristically mammalian structures. the epiphyses are 
Fic. 51.—Ventral view of skull of Hchidna aculeata, and right half of mandible. ang, 
Angle of mandible ; aud.oss, auditory ossicles ; cond, condyle of mandible; cur, 
coronoid process ; maa, maxilla ; o¢.cond, occipital condyle ; pal, palatine ; p.max, 
premaxilla ; pt, pterygoid ; sy, squamosal ; ty, tympanic ring. (After Parker and 
Haswell.) 
totally absent in Hehidna, and only to be seen in the tail-region 
in Ornithorhynchus. In having only the capitular head to the 
ribs, these mammals are evidently far removed from all other 
mammals, and are even more reptilian than the Theromorphous 
reptiles. The large clavicles and the interclavicle (Fig. 52, 
ee ee 
