168 ANATOMY OF THE WOOD RAT 



but the distance to the pomt at which the two fuse varies in 

 Homodontomys from 54.6 to 60 per cent the length of the 

 tibia; in Neotoma, from 62.3 to 64.2; and in Teonoma from 

 56 to 60.7 per cent. 



The head of the fibula, which is much the largest in 

 Teonoma, articulates with a process upon the caudal portion 

 of the lateral tuberosity of the tibia. The lateral part of the 

 head forms a well-marked process for the origin of the pero- 

 neus longus. Just mediad is a very faint process for the 

 origin of the peroneus digiti quinti, definable only in very 

 old individuals. With the latter may arise the peroneus 

 digiti quarti, or it may have origin from the ectal belly of 

 the peroneus quinti. The peroneus brevis takes origin from 

 the medial portion of the head along the medial border of 

 the shaft of the fibula. Upon the cranio-medial border, as 

 well as the adjoining part of the medial tuberosity, originates 

 the flexor fibularis, which may be responsible for a variably 

 roughened area situated craniad upon the distal shaft. 



At a point distad about two-thirds the length of the fibula 

 the latter joins the tibia, forming at this point the tibio- 

 fibular notch, and for some distance the two bones are 

 firmly ankylosed; but they may separate in the case of 

 specimens that have been cooked too long in cleaning. This 

 portion of the fibula appears as no more than a well-defined 

 ridge upon the shaft of the tibia, but the distal portion of the 

 fibula is really free from its neighbor for several milUmeters, 

 or at least very lightly attached. The distal termination 

 of the fibula broadens, and constitutes the external malleolus. 



Foot 



In man, supination of the foot is possible through about 

 60 degrees; pronation, on the average, probably not more 

 than 10; and rotation, without the aid of other movement of 

 this member, through something less than 90 degrees. 

 Certain individuals can surpass these figures, however, and 



