Mammalia. Monotremata. ,57 



the Pro-osteon, with both of which it is in relation, as in Birds and 

 most Eeptiles ; it is anchylosed at full growth with the Scapula. 

 The Epi-coracoid^ (as in Lizards) articulated with the anterior margin 

 of the Coracoid is also an osteological characteristic of this order. 

 The Clavicles are represented by two curved styles, extending from 

 the acromion along the transverse arms of the Interclavicle. In this 

 Order alone of all the Mammalia are the Inter clavicles found. The 

 Humerus is remarkable for its shortness and breadth ; both condyles 

 are remarkably produced, especially the internal one, which is 

 perforated. The Radius and Ulna are pretty firmly connected to- 

 gether through nearly the whole extent, the ulna being chiefly 

 remarkable for the olecranon, which is bent forwards upon the 

 humerus and transversely expanded at its extremity. The number 

 of Phalanges is the same as in other Mammals, thus preserving the 

 type notwithstanding the Sauroid tendency in the scapular arch. 



The Pelvic Arch and Appendages. The Pelvis resembles that of 

 the Marsupialia in the presence of the ''marsupial" bones, which 

 are however relatively larger and stronger in this order; and it re- 

 sembles that of Reptiles in the length of time during which the 

 three components of each os innominatum remain distinct. In the 

 great development of the Ileopectineal spine* of Ornithorhyncus com- 

 pare Tortoise. In the perforated Acetabulum of Echidna compare 

 Aves. The Femur is short, broad, and flattened ; the Fibula is longer 

 than the Tibia by the extent of a process which rises upward some 

 way above the point of articulation with tibia, and like the ole- 

 cranon is greatly expanded at its termination. Both Monotremata 

 have a sesamoid bone placed at the interspace between the astragalus 

 and the naviculare ; and a second supernumerary bone articulated 

 to the posterior part of the astragalus which supports the perforated 

 spur, characteristic of the male sex. 



See note on p. 56, 



* In the Macropidse this is also strongly developed. 



