THE BONES OP THE PELVIC LIMB 31 



hip bone), which joins its fellow of the opposite side ventrally at the symphysis 

 pelvis, and articulates very firmly with the sacrum dorsally. The two coxal bones, 

 together with the sacrum and the first three or more coccygeal vertebrge, constitute 

 the bony pelvis. The os cox® consists originally of three flat bones, the ilium, 

 ischium, and pubis, which meet at the acetabulum, a large cotyloid cavity with 

 which the head of the femur articulates. These three parts are fused before. growth 

 is complete, but are considered separately for convenience of description. The 

 ilium (Os ilium) is situated in the lateral wall of the pelvis, the pubis (Os pubis) in 

 the anterior part, and the ischium (Os ischii) in the posterior part of the ventral 

 wall. 



The thigh (Femur), hke the arm, contains a single long bone, the femur (or 

 thigh bone) (Os femoris). This articulates with the acetabulum above and the 

 tibia and patella below. 



The skeleton of the leg (Cms) comprises three bones (Ossa cruris), viz., the 

 tibia, fibula, and patella. The tibia is a large, prismatic long bone which supports 

 the weight, and articulates distally with the tibial tarsal bone. The fibula is 

 situated along the lateral border of the tibia, from which it is separated by the 

 interosseous space of the leg. It is much more slender than the tibia and does not 

 articulate ^vith the femur. In the pig and dog it has a complete shaft and two 

 extremities, but in the horse and ox it is much reduced and otherwise modified. 

 The patella (or "knee-cap") is a short bone which articulates with the trochlea of 

 the distal end of the femur; it is to be regarded as a large sesamoid bone intercalated 

 in the tendon of the quadriceps femoris muscle. 



The tarsus (or "hock") consists of a group of short bones, the ossa tarsi, 

 numbering five to seven in the different animals. The proximal or crural row con- 

 sists of two bones, the tibial and fibular tarsals ; the former is situated at the tibial 

 side, and has a trochlea for articulation with the distal end of the tibia; the latter, 

 situated at the fibular side, has a process, the tuber calcis, which projects upward 

 and backward and constitutes a lever for the muscles which extend the hock joint. 

 The distal or metatarsal row consists of four bones when seven tarsal elements are 

 present, as in the pig and dog. They are best designated numerically as first tarsal, 

 second tarsal, etc. The central tarsal is interposed between the rows. 



The preceding terms are anglicized abbreviations of those introduced by Gegenbaur into 

 comparative anatomy. The Latin names and synonyms are given in the foUo-ndng table: 



Tibial (Os tarsi tibiale, Tt.) Astragalus or Talus 



Fibular (Os tarsi fibulare, Tf.) Calcaneus or Os calcis 



Central (Os tarsi centrale, Tc.) Scaphoid or Navicular 



First Tarsal (Os tarsale primum, Tl) First or internal cuneiform 



Second Tarsal (Os tarsale secundum, T2) Second or middle cuneiform 



Third Tarsal (Os tarsale tertium, T3) Third or external cuneiform 



Fourth Tarsal (Os tarsale quartum, T4) Cuboid 



The metatarsal and digital bones resemble in general those of the corresponding 

 regions of the thoracic limb; the differential features will be noted in the special 

 descriptions. 



