156 Bulletin American Museum of Natural History. [Vol. XXVII, 



semicircular, oblitiue rather than vertical in position, connected with large 

 anterior process of malleus; ossicula auditus relatively large; stylomastoid 

 foramen present; 7 cervical and 19-20 dorso lumbar vertebrse; epij)ubic 

 bones (cf. Marsupialia) ; ilium trihedral, large pectineal tubercle on pelvis; 

 fibula expanding proximally; heel pointing downward. 



5. Specialized or aberrant characters. Among the very numerous fea- 

 tures belonging under this category are the following: the divergent modi- 

 fications of the snout in Ornithorhynchus and Echidna; lachrymal absent; 

 jugal absent (E) or vestigial; hard palate prolonged very far backward, 

 causing the pterygoids to approach the auditory region; palatine and ptery- 

 goid entering the floor of the brain case; olfactory opening single (O), 

 ethmo turbinals enlarged and extending backward below the olfactory 

 peduncle (£); malleus and incus firmly connected; no osseous arch above 

 the external auditory meatus; condylar foramen (in 0) fused with for. lac. 

 post; single olfactory foramen (0); canals for spinal nerves perforating 

 neural arch; no epiphyses on presacral vertebrje; ribs with reduced tuber- 

 cula; sternal ribs fully osseous (by ectostosis); scapula inclined sharply for- 

 ward; humerus with extreme development of crests; olecranon bifid; 

 femur (O) pointing almost directly outward; pes (0) pointing outward, 

 digits II-V curved backward; tarsal spur bone an enlarged tibial sesamoid; 

 astragalus bearing both tibia antl fibula; tuber calcis at right angles with 

 cuboid. 



j\Iany of the peculiar skull characters: such as the very broad condyles 

 nearly continuous across the basioccipital, the powerful mastoid processes 

 (which served for the attachment of heavy muscles) may possibly be a result 

 of primarily fossorial adaptations (p. IGl). 



Characters which demonstrate that the Monotremes are true 

 ■ Mammals. 



The numerous characters cited below (p. 157) which tend to connect the 

 INIonotremes with the Marsupials, reinforce other mammalian characters, 

 as follows: 



(1) Four optic lobes as in Mammals, contrasted with two in lower 

 vertebrates (Flower, quoted by Beddard, 1907, p. 110). 



(2) Jacobson's organ agreeing in its principal features with the mam- 

 malian type (Seydel, quoted by Weber, 1904, p. 323). 



(3) Alimentary canal showing "no great divergencies from the normal 

 structure" (Beddard, /. c, p. 109). 



(4) Liver with the usual mammalian subdivisions (Beddard, /. c, p. 1 10). 



