The Bones of the Pelvic Limb

The pelvic limb, like the thoracic, consists of four segments, viz., the pelvic girdle, thigh, leg, and the hind foot or pes; the last is subdivided into tarsus, metatarsus, and digits.

The pelvic girdle (Cingulum extremitatis pelvinæ) consists of the os coxæ or 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 two or three coccygeal vertebræ, constitute the bony pelvis. The os coxæ consists originally of three flat bones, the ilium, ischium, and pubis, which meet at the acetabulum, a large cotyloid cavity that articulates with the head of the femur. 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), like the arm, contains a single large, 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 (Crus) 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 below with the tibial tarsal bone. The fibula is situated along the outer 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 with 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 (Ossa tarsi) numbering five to seven in the different animals. The proximal or crural row consists of two bones, the tibial and fibular tarsals; the former is situated at the inner or tibial side, and has a trochlea for articulation with the distal end of the tibia; the latter, situated externally, 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 following 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, T1) 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.