Wyman.] 272 [Juno 5, 



ative position. For of all the means of determining homolooles, this 

 is the most trustworthy. If the two bones of the fore arm and of 

 the leg are placed in planes at right angles to the axis of the body, 

 those bones must be considered homotypes, which occupy correspond- 

 ing positions. The bone on the outside of the fore arm, a iz., the 

 radius, can only be the homotype of that on the outside of the leg, 

 viz., the fibula. But few anatomists have made any allowance for the 

 pronation of the fore arm, and most of them overlook the fx't that 

 the proper position of the bones of this segment for compari^on with 

 those of tlie leg, is supination. If the position of pronation is to be 

 retained for the fore arm, the leg should go through a corresponding 

 rotation in the opposite direction. Viewed in connection \'ith the 

 idea of symmetry, the homotypes are determined without dfficulty, 

 and are as follows : — 



The Radius is homologous with the Fibula. 



The Ulna is homologous with the Tibia. 



THE PATELLA. 



By Vicq d'Azyr, who has been followed by Meckel, Blainville, 

 Martins, Humphrey and others, this bone has been regarded as the 

 homotype of the olecranon, differing from it, however, in being at- 

 tached to bone by a ligament. Soemmering, who has been followed by 

 Berlin Bichat, Flourens, Owen and Cruveilhier, maintains that the 

 patella belongs to the class of sesamoid bones, and therefore, jn-operly 

 speaking, does not belong to the skeleton at all. 



We believe the latter view to be the correct one, for the same rea- 

 son, that the separate bone in the leg of the Wombat, already referred 

 to, is a true sesamoid, and not a detached epiphysis of the fibula. Mr. 

 Humphrey, like the others, who regard the radius as the homotype of 

 the tibia, and the olecranon as the homotype of the patella, is obliged 

 to meet the difficulty which arises from the connection of the patella 

 with the tibia, when, if it were the homotype of the olecranon, it 

 should be connected with the fibula. Mr. Humphrey admits the pos- 

 sibility of a part of a bone, an epiphysis, being detached, and of 

 becoming connected with another, and sustains his statement by the 

 analogy of the ribs, which, he says, may be transferred from the upper 

 to the lower transverse process, or vice versa.* This does not seem to 

 be an analogous case ; for, in point of fact, the typical rib is attached 

 to both, as, for example, in the foremost ribs of the alligator, and either 

 the upper or lower attachment may become obsolete, Avithout really 

 shifting the relation of the ribs to the vertebra. There is not a single 



* Memoir, p. 20. 



