Bones of Tarsus | Gross Anatomy | Anjani Mishra

GROSS STUDY OF TARSUS  

Bones of the Pes

Written By Anjani Mishra

Pes is the fourth segment of hindlimb/pelvic limb

It consists of three segments;

• Tarsus- consists of tarsal bones
• Metatarsus- consists of metatarsal bones
• Digit/digits- consists of phalanges and sesamoid bones

General plan for Tarsus (in domestic animals and birds) 

• A group of tarsal bones are known as tarsus.
• Tarsus is the first segment of pes.
• Tarsus consists of number of bones ranging from five to seven tarsal bones in domestic animals and in adult fowl the tarsus do not exist .
• These bones are arranged in three rows; i.e., proximal, central and distal row.
• The proximal row consists of two tarsal bones and are arranged from medial to lateral as tibial tarsal, and fibular tarsal.
• The central row consists of only one bone except ox where it is fused with 4th tarsal bone. 
• The distal row consists of two to four tarsal bones and are arranged in the same manner as first, second, third, and fourth tarsal bones except ox where first tarsal is on the lateral side.
• In case of fowl, the tarsus in the adult chicken does not consists of a group of small bones as in mammals. During fetal life the tarsus bone do exist in the two rows. The proximal row fuses with the tibia and the distal row fuses with the metatarsus.

Tarsus(ox)

• It is the first section of the pes and consists of five short bones, arranged in three rows; proximal, central and distal.
• The bones of tarsus are arranged between the tibia/fibula above and metatarsal bones below forming a hock joint.
• The bones of the proximal row (from medial to lateral) are: tibial tarsal(astragalus), fibular tarsal(os-calsis).
• Bones of the central row are: central & fourth fused tarsal(scaphocuboid).
• Bones of the distal row are: 2nd and 3rd fused tarsal(cuneiform magnum) on the medial side and 1st tarsal(cuneiform parvum) on the lateral side.

TIBIAL TARSAL:

• It is the medial bone of the proximal row and is somewhat compressed from before backwards.
• It has 6 surfaces.
• The dorsal and anterior surfaces are continuous and are articular. It is trochlear in appearance and articulates with the distal extremity of the tibia. A deep fossa is present at the anterior surface.
• The posterior surface is smooth and articulates with the fibular tarsal.
• The medial surface is slightly depressed, nearly flat about its middle, and marks a small tubercle above the depression.
• The lateral surface is irregularly concave and articular.
• The ventral surface articulates with central & 4^th tarsal, and is composed of two condyles separated by a groove.

Relations:

• Articulates proximally & anteriorly with the tibia.
• Articulates antero-laterally with the lateral maleolus.
• Articulates posteriorly with fibular tarsal.
• Articulates distally with central & 4^th tarsal.
• Articulates laterally with a part of fibular tarsal.

FIBULAR TARSAL:

• It is largest bone of the tarsus.
• It is elongated and flattened from side to side and is placed behind and lateral to the tibial tarsal.
• The body or the middle part is flat, the medial surface of which is slightly concave and lateral surface convex.
• The posterior border is nearly straight and gives attachment to planter ligament.
• The anterior ligament is slightly concave, smooth and rounded.
• The proximal extremity(tuber calcis) forms the point of hock and presents a depression for insertion of gastrocnmius tendon.
• Ventral extremity is irregular.
• Medially a strong, thick projection articulates with the posterior surface of tibial tarsal, known as sustentaculum tail.

Relations:

• Articulates anteriorly with the tibial tarsal.
• Articulates ventrally with a part of central & 4^th tarsal.
• Articulates medially with the lateral surface of tibial tarsal.
• Articulates dorsally with the lateral maleolus.

CENTRAL & FOURTH FUSED TARSAL:

• The central and 4^th tarsals are fused together to form a large single bone, which occupies the entire width of the tarsus and articulates with the bones of the joint.
• Dorsal surface is concave and smooth. There is spine at postero-medial angle of this surface.
• The ventral surface has two different levels for fusion with 4^th tarsal bone.
• The anterior and the medial surfaces are continuous, convex and rough.
• The lateral surface is very uneven and rough.
• The posterior surface is irregular and presents two tubercles ( lateral & medial).

Relations:

• Articulates superiorly with tibial & fibular tarsal.
• Articulates inferiorly with 2^nd & 3^rd fused tarsal and large metatarsal.
• Articulates posteriorly with 1^st tarsal.

FIRST TARSAL:

It is quadrilateral piece of bone placed at the postero-internal part of the tarsus.

Relations:

• Articulates dorsally with central & 4^th tarsal fused.
• Articulates ventrally with large metatarsal bone.
• Articulates anteriorly with 2^nd & 3^rd tarsal fused.

SECOND & THIRD TARSAL FUSED:

• It is small, flattened plate of bone placed under the ventral surface of central & 4^th fused tarsal.
• Dorsal surface is concave and articulates with the medial part of the ventral surface of the central & 4^th fused tarsal.
• Ventral surface is concavo-convex and articulates with medial facet on the proximal articular surface of the large metatarsal.
• The anterior and medial surfaces are continuous, convex, rough and non-articular.
• Lateral surface has small facet in front for articulation with central & 4^th fused tarsal.
• Posterior surface is narrow and has small facet for articulation with 1^st tarsal.

Comparison with:

A) Tarsus of Horse:

• It has 6 tarsal bones, namely: tibial, fibular, central, first & second fused, third and fourth tarsal.
• Tibial and fibular tarsal bones are shorter and thicker.
• Sustentaculum tali are stronger, longer and bear a facet in front of tibial tarsal.
• Central and third tarsal bones are flat in shape.
• First and second fused bone is small.
• Fourth tarsal bone is irregular.

B) Tarsus of Dog:

• 7 tarsal bones namely: tibial, fibular, central, first, second, third and fourth tarsal bones.
• Tibial tarsal has body, neck and head.
• Fibula tarsal is elongated and has a long process in front forming the beak.
• Sustantaculum tail are short and small.
• Central tarsal is concave above for articulation with head of tibial tarsal.
• First tarsal is irregularly quadrilateral and flat.
• Second tarsal is smallest bone of tarsus and is wedge shaped.
• Third tarsus is also wedge shaped.
• Fourth tarsus is very high and four sided.

C) Tarsus of Pig:

• Tarsal bones are seven in number as in dog.
• Tibial and fibular tarsal are similar in shape to that of ox.
• Second tarsal is small.
• Third and fourth are larger.

D) Tarsus of Rabbit:

• Tarsus bones are arranged in three rows.
• Proximal row ( two bones): Tibial and fibular tarsal.
• Middle row: central tarsal.
• Distal row (three bones): first & second fused, third and fourth tarsal.

E) Tarsus of Fowl:

• Tarsus appears to be absent in adult fowl.
• The proximal row unites with the tibia called tibio-tarsus.
• The distal row fused with metatarsus to form tarso-metatarsus.

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