POSTERIOR EXTREMITY. 47 



seven and a half. The articulating surfaces are separated by a broad 

 spine, which corresponds with the depression between the condyles. 



The upper part of the body of the tibia is very rough near the articula- 

 tion, especially at its outer part. In the midst of this roughness, posteriorly 

 and externally, is the articulating surface of the fibula, nearly three inches 

 long. The shaft of the bone presents three ridges : at the anterior is 

 situated the tuberosity of the tibia, which is of a triangular form, and 

 generally rough. On the inner part of this edge is an extensive rough 

 surface. The external edge of the shaft is quite sharp : beginning at the 

 external condyle, near the articulation of the fibula, it is rough ; near to the 

 middle of the bone, it becomes sharp and well defined, to terminate smooth 

 inferiorly in a considerable prominence connected with the lower extremity 

 of the fibula (Plates XIII. and XIY. A). The postero-internal edge is also 

 sharp and well defined at its upper extremity, continues so to the middle, 

 then becomes smooth, and terminates inferiorly in the malleolus interims. 

 This is a short thick protuberance, presenting a prominence for the attach- 

 ment of the great tibio-tarsal ligament. 



The upper extremity is in circumference thirty inches. The entire 

 length of the tibia is twenty-eight inches. The circumference of the middle 

 of the shaft measures thirteen inches and a half. The lower articulating 

 surface is about ten inches across. 



Fibula (Plate XXV. Fig. 5). — This bone occupies much the same rela- ribuia. 

 tive situation as in man, and is rendered, by the pointed extremity of the 

 external malleolus, of about the same length with the tibia. The upper 

 extremity of this bone is placed on the back of the tibia ; its posterior 

 external surface is very rough. The articulating surface is from two to 

 three inches in length. The body presents three ridges : an external, 



