﻿PELIS SPELvEA. 123 



spine (figs. 2, 3', e). They are deepened in the living animal by the semilunar cartilages 

 that form an elastic or variable socket, and, with the adipose ligament in front, make up a 

 broad articulation for the support of the hind quarters of the animal, which would other- 

 wise rest on mere points. At the intersection of the nearly plain tibial facets and the 

 highly convex femoral condyles, these cartilages are firmly fixed to both tibia and femur 

 by strong ligaments. The facets are separated posteriorly by a deep notch (fig. 2'/), in 

 which is implanted the posterior crucial ligament, and are strengthened laterally by the 

 external and internal tuberosities (fig. 2, g, h), affording attachment to the external and 

 internal lateral ligaments. On the under side of the external tuberosity is a small oval 

 articulation (fig. 2, g), for the head of the fibula, and under the posterior edges of the 

 same tuberosity is a groove for the semi-membranosus muscle. In front of the spine, 

 and forming a small shallow indentation in the anterior surface of the external facet, is a 

 roughened space of triangular form (figs. 2, 2', I) that extends inwards, so as to cut off 

 the internal facet from the base of the crest. It affords attachment to the adipose cushion 

 or ligament, filling the space between the tibia, the fore part of the distal articulation of 

 the femur, and the patella. A strong and massive anterior tuberosity forms the antero- 

 external boundary of the external facet (figs. 2, 2', m). The proximal end of the crest is 

 covered by a projecting and slightly roughened mass called the tubercle (figs. 2, 2', n), 

 which extends considerably downwards in the larger Eeles, and in the two bones at 

 Taunton of Felis spelaa, is nearly parallel to the posterior surface of the shaft. It 

 affords attachment to the patellar tendon, which, through the medium of the patella, is 

 the principal tendon of the muscles which act at once as the extensors of the tibia and 

 flexors of the femur. Many of these muscles are also partially attached to the head and 

 sides of the tibia, such as the rectus interims and sartorius, forming one muscle, the 

 fascialis, the rectus anticus, vastus internus, and semi-tendinosus while others, viz., the 

 arquatus, of Straus-Durckheim, the equivalent of the adductor magnus in Man, the popliteus 

 and semi-membranosus and triceps cruris, act as the extensores cruris and flexores tibise, 

 and leave their marks in the ridges and grooves on the posterior face of the bone. The 

 posterior angles of the prismatic portion of the shaft are termed the extero- and intero- 

 posterior crests (fig. 1', o,_p), the latter of which is traversed by a minute ridge, which is 

 the line of attachment of the inter-osseous membrane that binds the tibia to the fibula. 

 Near this and at a distance from the proximal end of about one third of the entire length, 

 is the small foramen for the passage of the nutritive artery and nerve. The outward 

 sweep of the crest (fig. 2, m) forms on the external surface a large concavity (fig. 2, q), 

 affording origin to the large tibialis anticus, which acts as a flexor of the foot and extensor 

 of the toes. A considerable portion of the length of the shaft is occupied by the origin 

 of the flexor longus digitorum on the inner side, the tibialis posticus running in a parallel 

 direction on the external surface close to the inter-osseous membrane. 



The shaft increases in size as it approaches the distal articulation (figs. 1, 1", r, s), 

 which is of somewhat trapezoidal form, wider than deep in a vertical direction, divided 



