152 Bulletin American Museum of Natural History. \\o\. XXVII, 



Vertebral column, limbs. 



Axis. Anterior facet of odontoid Avith a ventral extension very similar 

 to that in Ci/nognathus (Primitive). 



Cervical vertebra' without autogenous transverse processes but with true 

 cervical ribs (primitive), as in Reptilia, which remain suturally separate 

 from the centrum till late in life. (Unique among mammals, save that in 

 PerameJes the transverse process of the axis is also rib-like.) These cervical 

 ribs have a capitular and a tubercular portion between Avhich runs the 

 vertebral artery, which perforates the seventh cervical (as well as C 2-6), as 

 it does in ^Marsupials. 



Dorso-lumbar -vertebrae. The nvmiber of these vertebrte to be assigned to 

 jNIonotremes depends upon the interpretation of the sacrals. Howes (1885, 

 p. 89) gives 4 sacrals to Echidna and 3 to Ornithorhi/ncJnis. In that case 

 both genera would have 19 dorso lumbar vertebrae {ProecJtidna 20) a number 

 characteristic of primitive IMarsupials. But in the view of the writer the 

 anterior "sacral" is only a slightly modified lumbar and the posterior sacral 

 only a slig-htlv modified caudal. In that case the vertebral formulae would 

 be as follows: Ornithorhynchus C. 7, D. 17, L. 2, S. 1, CS. 1, Cd 19; 

 Echidna C. 7, D. 10, L. 5, S. 2,— , C 10. 



In the dorsal vertebrw "the canals for the exit of the spinal nerves perforate 

 the neural arch " instead of issuing between the vertebme (F'lower, 1885, 

 p. 65) (Unic[ue ?). 



Epiphyses. There are no epipJii/scs on the })resacral vertebrae. (Second- 

 ary, cf., Sirenia, but of uncertain adaptive significance.) 



Ribs with reduced tubercula, not articulating with transverse processes 

 but attached to centra only, "the greater part of the articular surface being 

 below the neuro-central suture, the reverse of what occurs in the higher 

 Mammals" (Flower, /. c. p. 65). (Possibly reptilian in part.) 



Sternal ribs. Becoming fully osseous as in Armadillos, but very peculiar 

 inasmuch as they ossify l)y ectososis, as in Birds (Parker, quoted by Flower, 

 I.e., p. 119). 



Fore limb. The position of the fore and hind limbs is unique among 

 mammals. The scapula is inclined forward, overlapping the neck vertebrae. 

 The extreme forward inclination is probably secondary (pp. 119, 433). The 

 humerus, instead of facing forward and downward as in other mammals, 

 faces inward and downward (partly primitive, partly aberrant). The 

 elbow is turned sharply outward. The glenoid fossa of the scapula is close 

 to the mid-line of the stermun instead of being widely removed from it as 

 it is in other mammals. This condition is correlated with the large size of 

 the coracoid and procoracoid (Primitive). 



