Digits of Forelimb | Gross Anatomy | Anjani Mishra

GROSS STUDY OF MANUS (DIGIT/DIGITS)

Written By Anjani Mishra

DIGITS (OX)

• Digit/digits are the third section of manus which is four in number in ox.

• The digit or digits are the collective name of first phalanx, second phalanx, and third phalanx.

• The large metacarpal bone, separates at the distal extremity into two condyles and each condyle carries one digit and each digit carries three phalanges and three sesamoid bones.

• In ruminants (cattle, sheep, and goat), there are four digits in each leg of forelimb, namely; second, third, fourth, & fifth.
• Among these, third and fourth digits are well developed and carries three phalanges and three sesamoids each.
• The second and fifth are vestiges represented only by small dew claws at the back of fetlock joint; each contains one or two small bones which do not articulate with the rest of the skeleton.

THE FIRST PHALANX (Os Suffraginis)

Shape: It is long bone, more or less cylindrical.

Location: Placed between large metacarpal above & second phalanx below.

Direction: Placed obliquely downward & forward.

Articulation: It articulates proximally with the distal extrimity of metacarpal and proximal sesamoid bones forming a fetlock joint and distally with the second phalanx forming a pastern joint.

 

Composition: It presents a shaft & 2 extremities

A) Shaft:

• Thicker above than below.
• The anterior surface is rounded from side to side and blends with the lateral         surfaces.  
• The posterior surface is irregularly depressed and has nodular elevation at middle on either side for the ligamentous attachment.
• The interdigital surface, which is nearly, flat and rough. The proximal inter-digital ligament is attached to this area.

B) extremities: two 

Proximal extremity

• It is larger than distal extremity, and articulates with the distal extremity of large metacarpal bone.
• It presents an articular surface, which is concave form before backward and is divided into two areas by an antero-posterior deep groove.
• The lateral articular surface is larger and higher in level then medial surface.
• Behind the articular area there are two facets for articulation with the proximal sesamoid bones.

Distal extremity

• It is smaller than the proximal extremity and articulates with the proximal extremity of the second phalanx.
• The surface is divided by an antero-posterior groove into two condyles. The lateral is larger than medial.

                            

THE SECOND PHALANX (Os Corona)
 

Shape: it is a long bone, more or less cylindrical and contains a small medullary cavity.
Location:  Placed between first phalanx  above & third phalanx below.

Direction: Placed obliquely downward & forward.

Articulation: It articulates proximally with the distal extrimity of first phalanx forming a pastern joint and distally with the third phalanx and distal sesamoid bone forming a coffin joint.  
                               

Composition : It presents a shaft & 2 extremities

 A) Shaft:

•  Has three sides
• The posterior surface is nearly flat or slightly concave.
•  It is rendered short by the encroachment of the distal articular surface.
• The lateral surface is convex, rounded and rough for ligamentous attachment.
• The interdigital surface is depressed.

B) extremities: two 

Proximal extremity

•  It presents an articular surface, which is divided by an antero-posterior faint ridge into  two concave areas, the lateral of which is larger and lower in position than the medial.
• The articular surface, anteriorly, forms a prominent projection.
•  Posteriorly, there are two tubercles and a depression, which are intended for the attachment of the tendons of the superficial digital flexor muscle.                              

Distal extremity:

• It is condyloid and is divided by an antero-posterior groove into two articular area, the lateral of which is larger than the medial.
• The articular surface encroaches considerably on the anterior and posterior surfaces.

THE THIRD PHALANX (Os pedis)

•  It is the terminal bone of each digit and is enclosed entirely by hoof with which it bears close resemblance.
• Proximally, it articulates with the distal end of the second phalanx.

Composition:  the bone presents, 4 surfaces and 6 borders.

  A) Surfaces:

1)Lateral surface :

•  It is rough and traversed a little below its middle by a shallow groove running antero-posteriorly along which there are large numbers of foramina.
• The area below the groove is prominently raised, rough and porous while the area above the groove is rough and perforated by a number of small foramina.
• The posterior part is very steep.

2. The medial/ Inter-digital surface:

•  It is smooth and is marked by an antero-posterior groove along which there are  a large  number of foramina
• The part above the groove is rough and porous.

3)The ventral /Sole surface

        It is nearly flat being slightly concave in front.

4) The dorsal /Articular surface:

• It is concave and slopes downward and backward.
• It is divided by an antro-posterior faint ridge into two areas, of which, the lateral being larger & higher in level than medial.
• It presents posteriorly a trsnsverse concave facet for articulation with distal sesamoid.

B) Borders: 

1)     Anterior border: it is vertical, slightly convex and sharp.

2)     Dorso-lateral  border: It is convex &separates the articular and lateral surfaces.

3)     dorso-medial borer: It is convex& separates ventral and lateral surfaces

4)     ventor-lateral border: It is convex & separtes ventral sufaces.

5)     ventro-medial border: It is nearly straight and sharp & separates the  medial and ventral surfaces.

6)     posterior border: It is thick and rounded.

Comparison with:

a)     phalanges of horse:

• There is only one digit, which consists of three phalanges as 1^st,2^nd & 3^rd  phalanx.        1^st phalanx:
• It is longer than that of ox and is singal. Facets for proximal sesamoids are absent.             2^nd phalanx:
• It is also single, antero-posterioly compressed and longer than of ox.   
• 3^rd phalanx: 
•  It presents 3 surfaces, 3 borders & 2 angles.
•  It is single bone and resembles the shape of hoof, as it is encloded within the hoof.

b)     Phalanges of Dog

• The first digit has only two phalanges due to which this digit fails to contact with ground while walking.
• The rest of digits have three phalanges each.
• 3^rd &4^th digits are largest.
• The two phalanges of the first digit resemble with the 1^st & 3^rd  phalanges of other digits.
• The1^st& 2^nd phalanges are the longer bones. The shaft of 1^st phalanx of all digits (except the first) is four sided and is slightly bend.
• The 2^nd  phalanges are about two-third of first, in length.
• The 3^rd phalanx, which resemble to the claws, are hook like. 

c)      Phalanges of Pig:

• Each digit has three phalanges.
• The phalanges of 3^rd &4^th digit are well developed.
• The phalanges of 2^nd & 5^th digit are small and generally don’t reach to the ground.

d)     Phalanges of fowl:

       There are three digits in numbers and are present at the terminal segment of the
     wing.
     The 2^nd and 3^rd digits consist of two phalanges and 4^th digit has only one phalanx.
     3^rd digit is the largest.
  

   Fig: Radius-ulna and manus showing phalanges of chicken

11. Second digit (phalanges first and second)
13. Third digit (phalanges first and second)
14. Fourth digit (first phalanx)   

 The SESAMOIDS (OX)

• Sesamoid bones are arranged in two rows, namely; proximal and distal rows.
• Proximal sesamoids are situated behind the proximal end of first phalanx at the level of metacarpo-phalangeal articulation or fetlock joint.
• Distal sesamoids are situated behind the distal phalangeal articulation in between the second and third phalanx at the level of pastern joint.
• These are small bones and may be included in the group of short bones.

Proximal Sesamoids:

• The proximal row consists of two bones for each digit. 
• The total number of sesamoid is four, two for each digit in one limb.
• The bones of each pair articulate with the corresponding part of the distal end of the large metacarpal bone by their dorsal surface, with each other and with the 1^st phalanx by small facets.
• The apex is pointed dorsally and a slip of suspensory ligament is attached to it.

Distal Sesamoid:

• The distal row consists of one bone for each digit.
• The total number of sesamoid is two, one for each digit in one limb.
•  It is short bone and is placed transversely behind the distal phalangeal articulation.
•  Their ends are narrower than proximal.

Comparison with:

A) Sesamoids of Horse:

•   There are two proximal sesamoids in each limb and much larger than those of ox.
•   These are pyramidal in shape.
•   The two sesamoids articulate with the large metacarpal but don’t articulate with each   other or with 1^st phalanx as in ox.
•   The distal sesamoid is single and is shuttle shaped known as "navicular bone". It is  larger and longer than that of   the ox.

B) Sesamoids of Dog:

•  Proximal sesamoids are anterior and posterior.
• Anterior sesamoids are five in number and each is in the form of a nodule in metacarpo-phalangeal joint of each digit.
• Two posterior sesamoids are present behind each  metacarpo-phalangeal joint form  2^nd to the 5^th digit while 1^st digit usually has single, flattened sesamoid; exceptionally, two are present.
• The distal palmar sesamoids remain cartilaginous.

C)  Sesamoids of Pig:

•      There are two proximal and one distal sesamoid bones in each chief digit where as each accessory digit comprises two proximal sesamoid bones only.

Notes:

• Cow, sheep & goat have two principal digits or toes; the 3^rd & 4^th, while the 2^nd & 5^th    digits are represented only by small dew claws.
•  In the pigs the dew claws are much better developed and are 2^nd & 5^th digits.
• The dogs normally have 5 digits on each fore limb. The 1^st digit is only dew claw and   corresponds in position of human thumb.

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