146 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [YoLYI. 



a narrow bony span, arclied outwardly, that holds the tendons of the deep 

 extensors in position. 



The inner end of this arch is the higher on the bone, and just above 

 it, on the shaft, we find a minute tubercle, that gives attachment to a lig- 

 ament tJiat is extended to another tubercle lower down on the shaft, and 

 on the opposite side. 



The fibula is the merest apology for a bone, represented only by a 

 slender spine on the outer side of the tibia. It has a superior and knob- 

 like head, that articulates with the horizontally expanded head of its 

 sizable companion ; lower down it meets the fibular ridge, and is firmly 

 attached to it by a strong, fibrous, and close-fitting connection. 



Below the ridge the fibula is continued, hair-like in dimensions, to meet 

 the tibia below the middle of its shaft, to become thoroughly and indis- 

 tinguishably confluent with it. 



The patella (PI. IV, Fig. 22) is a free bone, and is found in the ten- 

 don of the quadriceps extensor. It is compressed antero-posteriorly, 

 with an elliptical base above. 



From the points representing the vertices of the major axis of this 

 ellipse, bounding lines pass, to meet broadly concave below. The ante- 

 rior surface, limited by these boundaries, is convex outwards; the pos- 

 terior surface, slightly concave, is divided by a vertical ridge into two 

 unequal parts, the outer of which is the greater. The femur averages 

 2 centimetres in length, the tibia 3.2 centimetres, and the bone now to 

 be described as the tarso-metatarsus nearly 2.3 centimetres, falling be- 

 tween the thigh and leg-bone. 



The metatarsals of the second, third, and fourth toes, and certain tar- 

 sals at the upper extremity of the bone, coalescing, form the segment, 

 tarso-metatarsus J next in order below the tibia, with which it articulates. 



The articular surface of its summit is so arranged as to accommodate 

 itself to the condyles of the tibia, consisting essentially of an inner and. 

 outer antero-posterior facet, and a prominent spine on the anterior mar- 

 gin, that accurately fits in the intercondyloid notch 6'f the bone above. 



On the posterior aspect of the bone above we find the " calcaneal " 

 process, here approaching a right parallelopiped in form, being vertically 

 pierced by four minute cylindrical canals, two next the shaft and two 

 parallel with them and above. They are for flexor tendons, which pass 

 through them. The shaft is straight, subcylindrical, and hollow, ex- 

 panding below for the trochlese for the phalanges. For its upper half 

 and posteriorly, ranging below the calcaneal process, it develops a sharp 

 vertical crest, that gradually subsides below. 



The anterior aspect of the shaft is faintly grooved longitudinally, 

 and where it dies out below, just above the notch between the third and 

 fourth terminal trochleas, we observe a minute perforating foramen for 

 the anterior tibial artery. Upon the inner margin of the shaft below 

 there is the well-marked though shallow facet for the os metatarsale acces- 

 sorium. This diminutive bone is, as usual, slung to the tarso-metatar- 



