The Forelimb
5.2 Bones of the Thoracic Limb
Goal: Identify the major bones of the tho- racic limb and their features. Compare with bones of the thoracic limb of the horse and other small animals (e.g., dog).
Use the ox skeleton and the figures provided here to study the bones of the thoracic limb (Figure 5.1). The bones of the goat and sheep thoracic limb are like those of the ox.
5.2.1 Scapula
The scapula is a flat, roughly triangular bone of the shoulder region. It is very similar to that of the horse except for one feature. The acromion is present in the scapula of rumi- nants but is absent in the scapula of the horse and pig. The lateral surface of the scapula has a large infraspinous fossa and relatively small supraspinous fossa (Figure 5.2).
The “shoulder blade” is a common name for the scapula which you may hear in the clinic.
The scapula has three borders (dorsal, cra- nial, and caudal), three angles (cranial, cau- dal, and ventral), and two surfaces (medial and lateral). The lateral surface has the spine of the scapula that separates the supra- and infraspinous fossae. A prominence in the middle of the spine is the tuber of the spine of the scapula: the tuber spinae scapulae.
The depression on the distal end (ventral angle) of the scapula is the glenoid cavity.
● Know the nomenclature for vessels and nerves on the dorsal and palmar aspects of the large metacarpal bone and digits.
● Understand the clinical signs associated with nerve damage (e.g., damage to radial and suprascapular nerves).
● Identify and know the clinical importance of superficial veins (i.e., cephalic, accessory cephalic, and dorsal common digital vein III). The superficial veins of the forelimb are
used for injection of antibiotics and for ret- rograde anesthesia.
● Know some of the clinical aspects (e.g., corkscrew, interdigital dermatitis, interdigi- tal phlegmon, and interdigital hyperplasia) associated with damage to the hoof and its contents (digital cushion, superficial and deep digital flexor tendons, navicular bursa, navicular bone), and the proximal and distal interdigital ligaments that join the weight- bearing digits together.
The glenoid cavity articulates with the head of the humerus to form the shoulder joint.
Use Figure 5.2 to study the main features of the scapula.
On the medial surface of the scapula, identify the subscapular fossa and the serrated face.
The supra- and infraspinous fossae are for attachment of the supra- and infraspinatus muscles, respectively. The subscapular fossa is for attachment of the subscapularis mus- cle, and the serrated face is for attachment of the serratus ventralis muscle.
Scapula
Humerus
Radius
Ulna
Carpus Metacarpal bones III
Accessory carpal bone and IV (large metacarpal bone) Phalanges
Proximal sesamoids Distal sesamoid Shoulder joint
Elbow joint Cranial part
of greater tubercle (point of the
shoulder) Olecranon tuber
(point of the elbow)
Ox
Figure 5.1 Bones of the bovine thoracic limb: left lateral view. Forelimb regions are the shoulder (scapula), brachium (humerus), antebrachium (radius and ulna), and manus (carpus, metacarpals, and digits).
Cranial border Serrated
face
Acromion Supraspinous fossa Subscapular
fossa Infraspinous
fossa
Glenoid cavity Ventral angle
Medial view Lateral view
audal C bor
der
Cranial angle Caudal
angle
Dorsal border Dorsal border
* *
Ox Caudal
angle
Caudal border Scapular spine (spine tuber)
Figure 5.2 The left bovine scapula: medial and lateral views * Supraglenoid tubercle.
In the live animal or fresh specimen, the dorsal border of the scapula has a large scapu- lar cartilage that extends its length dorsally.
5.2.2 Humerus
The humerus forms the bone of arm or bra- chium. It is a very strong and robust bone in both cattle and horses. There are minor dif- ferences in the shape of the humerus between small and large ruminants which will not be discussed.
In the proximal part of the humerus, note that the greater tubercle (point of the shoul- der) is well developed and deviates toward the medial side (Figure 5.3). It is larger than the lesser tubercle located on the medial side. The greater tubercle is located at higher level than the head of the humerus. The round head of the humerus articulates with the glenoid cavity to form the shoulder joint.
Both the greater and lesser tubercles are divided into cranial and caudal parts.
In the horse, the greater and lesser tuber- cles are mostly equal in size. In addition, the horse has an intermediate tubercle. No inter- mediate tubercle is present in ruminants.
The deltoid tuberosity on the lateral sur- face of the humerus is well developed in both
the cow and horse. It is the site for attach- ment of the deltoideus muscle.
Use Figure 5.3 to study the major bony prominences on the proximal and distal parts of the humerus. On the proximal humerus, identify the greater and lesser tubercles and intertubercular groove. The tendon of biceps brachii muscle passes in this groove.
Identify the brachialis groove, the attach- ment site for the brachialis muscle. The humeral crest forms the cranial border of this groove. The body (shaft) of the humerus is the part between the proximal head and distal humeral condyle.
On the distal humerus, identify the palpable medial and lateral epicondyles. The radial fossa is the shallow depression on the cranial surface of the humeral condyle. The relatively deep depression on the opposite caudal side of the humeral condyle is the olecranon fossa.
The condyle of the humerus articulates distally with the radius and ulna to form the elbow joint.
Humeral condyle Lesser (minor) tubercle
Deltoid tuberosity Greater (major) tubercle Cranial and caudal parts Femoral head
Olecranon fossa Lateral epicondyle
Intertubercular groove
Attachment site for infraspinatus m.
Deltoid tuberosity
Teres major tuberosity Humeral crest
Cranial
Greater (major) tubercle
Radial fossa
Ox
Caudal Lateral
Body (shaf t)
Brachialis groo ve
Figure 5.3 Left humerus of the ox: cranial, caudal, and lateral views.
Box 5.1
The greater tubercle of the humerus is palpa- ble in the live animal and forms the point of the shoulder.
5.2.3 Radius and Ulna
The radius and ulna are the bones of the antebrachium or forearm. Note that the ulna is complete in ruminants compared to that of the horse. The ulna in the ox is fused to the radius except for proximal and distal interos- seous spaces (Figure 5.4). In the horse, the ulna ends in the middle of the antebrachium.
On the proximal ulna, and with the help of Figure 5.4, identify the olecranon tuber or (tuberosity), the palpable point of the elbow in the live animal, the trochlear notch, and the anconeal process. The olecranon tuber- osity and anconeal process form the olecra- non. The olecranon tuberosity is the attachment site for the extensor muscles of the elbow (e.g., triceps brachii and tensor fas- ciae antebrachii).
The distal extremity of the ulna is called the lateral styloid process or styloid process of the ulna. In the horse, the styloid process of the ulna is developmentally fused to the radius.
The radius is shorter and thicker than the ulna. Near the proximal extremity (head), identify the radial tuberosity on the medial side. The head of the radius and the trochlear
notch of the ulna articulate with the humeral condyle to form the elbow joint.
The distal medial end of the radius is the styloid process of the radius (Figure 5.4).
The distal articular ends of the radius (trochlea) and ulna articulate with the proxi- mal row of carpal bones to form the radio- carpal joint.
5.2.4 Carpus (Proximal and Distal Rows) The bones of the carpus, metacarpus, and phalanges are known as the manus. At the end of this unit watch video 12.
As in the horse, the carpus in ruminants is composed of two rows (Figure 5.5a). The proximal row is like that of the horse and contains four bones. From lateral to medial, these are the accessory carpal, ulnar,
Olecranon tuberosity Anconeal
process
Proximal interosseous
space
Distal interosseous
space Styloid process of the ulna
Trochlear notch
of theBody radius
of theBody radius
Styloid process
of the ulna Styloid process
of the radius
Olecranon Olecranon
Head
Lateral Cranial Caudal
Radial tuberosity
Ox
Figure 5.4 Left bovine radius and ulna: lateral, cranial, and caudal views.
Box 5.2
The olecranon tuber is palpable in the live ani- mal and forms the point of the elbow. The point of the elbow approximates the distal part of the 5th intercostal space in the live animal.
intermediate, and radial carpal bones (Figure 5.5a). The accessory carpal is a pal- pable landmark on the lateral surface of the carpus. It provides an attachment point for
the ulnaris lateralis and flexor carpi ulnaris muscles.
The distal row is composed of two bones in ruminants. From lateral to medial, these are
2+3 4
R I U 4 2+3
I R
Metacarpal tuberosity
Dorsal and palmar longitudinal grooves (a)
(b)
IV III III IV
Accessory carpal bone
U Dorsal
view
Palmar view
L M
M L
Ox
Metacarpal bones III and IV Accessory carpal
bone Ulnar carpal
bone Radius
Ulna
Intermediate carpal bone Carpal bone IV Metacarpal bone V
Radius
Ulna
Metacarpal bone V Radiocarpal
joint
Midcarpal joint carpometacarpal
joint
Ox
1 2 3
Figure 5.5 (a) The left bovine carpus and proximal metacarpal region: dorsal and palmar views. The carpus has two rows. The proximal row contains four carpal bones: accessory carpal (AC), ulnar (U), intermediate (I), and radial (R), from lateral (L) to medial (M). On the dorsal view, the accessory carpal bone is obscured but can be seen on the palmar view palmar to the ulnar carpal bone. The distal row contains two bones, the fourth carpal and fused second and third carpal bones. The distal row articulates with fused metacarpals III and IV (large metacarpal bone). Rudimentary metacarpal V is shown in (b). (b) Lateral (left) and laterocaudal (right) views of bovine left carpus showing metacarpal V bone. 1, radiocarpal joint; 2, mid-carpal joint; 3, carpometacarpal joint.
the fourth carpal and fused second and third carpal bones (Figure 5.5a). Carpal one is not present.
The horse has three or four bones in the distal row including the fourth, third, second, and first carpal bones from lateral to medial, respectively. The first carpal bone in the horse may be absent, as in ruminants.
Articulation between the proximal and dis- tal rows of carpal bones forms the midcarpal joint. The articulation between the distal row of carpal bones and the large metacarpal bone (fused III and IV metacarpals) forms the carpometacarpal joint.
5.2.5 Metacarpal Bones (Large Metacarpal or Cannon Bone)
Metacarpals 3, 4, and 5 (Mc III, Mc IV, and Mc V) are present in ruminants. Mc III and Mc IV are fused forming a single large meta- carpal bone (Figures 5.5 and 5.6). Identify the metacarpal tuberosity on the proximo- medial surface of the large metacarpal bone.
This is the attachment site for the tendon of the extensor carpi radialis muscle.
In the horse, only the Mc III (cannon bone) is present. Because of the presence of two
weight-bearing digits in ruminants, the distal end of the large metacarpal bone has two parts with an articulating trochlea at each end. The space formed by this separation is the intertrochlear notch. Each trochlea articulates with the proximal phalanx (P1) of the corresponding digit.
The term cannon bone is a common name used for the third metacarpal (Mc III) bone in horses but also for the large metacarpal or fused Mc III and Mc IV bone in ruminants.
In ruminants, a small metacarpal 5 (Mc V) is present as rudimentary bone on the proxi- molateral aspect of fused Mc III and Mc IV (Figure 5.5b). You should not confuse Mc V with a fracture or bone growth when exam- ining an X-ray of ruminant carpal–metacar- pal regions.
The axial line of fusion of Mc III and Mc IV forms the dorsal and palmar axial longitu- dinal grooves (Figure 5.6). In the live animal, blood vessels occupy the dorsal and palmar metacarpal longitudinal grooves. The dorsal longitudinal groove is more distinct than the palmar groove.
Note the proximal and distal metacarpal canals (openings) at the proximal and distal ends of the longitudinal grooves (Figure 5.6).
III IV
Metacarpal tuberosity
Intertrochlear notch
Trochlea III IV
2+3 4 Dorsal axial
longitudinal groove Metacarpal
Digit III
tuberosity
Proximal and distal metacarpal canals
R I U
Proximal phalanx (P1)
Middle phalanx (P2)
Distal phalanx (P3)
Digit III
M L
M L
Digit IV
Ox
Figure 5.6 Bovine left manus (carpus, metacarpals, and digits): dorsal view. The image on the left shows articulation of the large metacarpal bone with the carpus proximally, and digits III and IV distally. The image on the right shows an isolated bovine large metacarpal bone. Each digit has a proximal (P1), middle (P2), and distal phalanx (P3).
These canals allow for passage of blood ves- sels between the dorsal and palmar sides of the large metacarpal bone.
5.2.6 Digits
Limbs of domestic ruminants have two digits.
The medial digit (digit III) and lateral digit (digit IV) are weight-bearing (Figure 5.6).
The medial and lateral dewclaws form digit II and digit V, respectively. They are non- weight-bearing in cattle and may not have bony skeleton. Skeletal elements of these dig- its are present in some ruminants.
The weight-bearing third and fourth dig- its have three phalanges each. From proximal to distal, these are proximal (P1), middle (P2), and distal (P3) phalanges (Figure 5.6).
Each phalanx is divided into base, body, and head, from proximal to distal.
The P1 and P2 are similar in shape but the length of P1 is twice as long as P2. The shape of P3 (coffin bone) is different from P1 and P2 (Figure 5.7).
Identify the extensor process on the prox- imodorsal surface of P3. This is the site for attachment of the axial extensor tendons from the common digital extensor muscle. A similar arrangement occurs with the axial extensor tendons of the long digital extensor tendons in the hind limb.
The common name for the distal phalanx (P3) is the coffin bone because it is embed- ded inside the hoof capsule analogous to a coffin.
Each digit has two proximal sesamoid bones (at the palmar surface of fetlock joint) and a single distal sesamoid bone (at the palmar surface of the coffin joint). Overall, a total of four proximal sesamoid bones and two distal sesamoid bones are present in the two weight-bearing digits of each limb (Figure 5.7). The navicular bone (analogous to a boat) is a common name for the distal sesamoid bone.
The nomenclature and general shape of the bones in the single digit of the horse is gener- ally like a single digit (III or IV) in ruminants.
Bones of the hind limb digits are like those of the forelimb.
The articulation between fused Mc III and Mc IV and P1 on each digit forms the meta- carpophalangeal joint (MCP) or the fetlock joint. Distal to the fetlock joint is the proxi- mal interphalangeal joint (PIP) or pastern
Metacarpal bones III and IV
Proximal sesamoids Proximal
phalanx Middle phalanx
Distal phalanx
(a) (b)
Distal sesamoids Intertrochlear notch Distal
metacarpal canal
Ox
Metacarpophalangeal joint
Proximal sesamoid Proximal interphalangeal
joint Distal sesamoid Distal interphalangeal joint
Proximal phalanx Middle phalanx Distal phalanx Metacarpal bones III and IV
Ox
Palmar view Lateral view
Figure 5.7 The left bovine digits: (a) palmar and (b) lateral views. In the live animal, digit IV (lateral) and digit III (medial) are interconnected by proximal and distal interdigital ligaments.
Box 5.3
The axial dorsal and palmar longitudinal grooves on the large metacarpal bone (fused Mc III and IV bones) can be seen as an opaque fusion in the midline on X-ray films. This should not be confused with a fracture.
joint formed by articulation of P1 with P2.
More distally, articulation of P2 and P3 forms the distal interphalangeal (DIP) or the coffin joint.