Veterinary Gross Anatomy

HUMERUS
(Ox, Sheep and Goat, Horse, Pig, Dog, Rabbit, Fowl)

Ox

• It is a long bone placed obliquely downward and backward between the shoulder joint above and the elbow joint below.
• It has a shaft and two extremities.

• Shaft: 
  • It has a twisted appearance and has four surfaces.
  • The anterior face is triangular, wide and smooth above, narrow and rough below.
  • The posterior face blends with the medial and lateral faces. It presents the nutrient foramen about the middle.
  • The medial face is nearly straight in its length. Just above its middle it presents the teres tubercle for latissimus dorsi and teres major.
  • The lateral face is spirally curved and forming the musculo-spiral groove, which contains the brachialis muscle. The groove is continuous with the posterior face above and winds around towards the front. Lateral surface is separated from the anterior by a distinct border the crest of humerus, which bears above its middle the deltoid tuberosity. The crest is for the insertion of brachio-cephalicus and superficial pectoral and the deltoid tuberosity for the deltoideus muscle. A curved line extends upward from the deltoid tuberosity and is for the lateral head of triceps. At the upper part of the curved line is a nodule for the teres minor.
• Proximal extremity:
  • It consists of a head, neck, two tuberosities and the intertuberal or bicipital groove.
  • The head presents a circular articular surface, which articulates with the glenoid cavity of the scapula to form the shoulder joint.
  • The lateral tuberosity consists of two parts - an anterior summit arching medially and a posterior convexity. The former over-hangs the bicipital groove and gives attachment to the lateral tendon of the infraspinatus. The convexity gives attachment medially to the medial tendon of the infraspinatus.
  • The medial tuberosity is smaller and consists of anterior and posterior parts. The anterior part forms the medial boundary of the intertuberal groove and gives attachment to the medial tendon of supraspinatus and to the deep pectoral. The posterior part is for the subscapularis.
  • The intertuberal groove is bounded by the anterior divisions of the two tuberosities and in life, is covered by a fibro cartilage for the play of the tendon of origin of biceps brachii.
• Distal extremity:
  • It has an oblique surface, which is divided by a ridge into two condyles, the medial being the larger. The medial condyle is crossed by a groove, which extends into the olecranon fossa and articulates with the semilunar notch of the ulna.
  • This extremity presents anteriorly above the articular area, the coronoid fossa, which receives the coronoid process of the radius in extreme flexion of the elbow joint.
  • Behind and above the condyles are two thick ridges, the epicondyles. The medial epicondyle is more prominent and furnishes origin to flexor muscles of the carpus and digits and bears a tubercle for the attachment of medial ligament of the elbow joint. The margins of the olecranon fossa are for the origin of the anconeus. The lateral epicondyle bears laterally the condyloid crest in the form of a raised ridge, which gives origin to extensor carpi radialis. Between these two epicondyles is the deep olecranon fossa, which receives the anconeus process of ulna during extreme extension. The distal extremity also presents a rough depression laterally and a tubercle medially for the collateral ligaments of the elbow joint.

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Sheep and Goat

•  It is relatively longer and slender than that of ox.
• The deltoid tuberosity is closer to the proximal end and not as prominent.
• The lateral tuberosity is smaller and does not overhang the bicipital groove.
• Olecranon and coronoid fossa are shallower.

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Horse

• The deltoid tuberosity is more prominent.
• The bicipital groove is divided by intermediate ridge.
• The summit of lateral tuberosity does not arch inward.
• The coronoid and the olecranon fossa are shallower.

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Pig

• It has the appearance of italic letter ‘f’ minus the cross bar.
• The shaft is laterally compressed and flat on the medial side.
• The musculo-spiral groove is shallow and the deltoid tuberosity is small and there is a larger rounded eminence midway between it and the lateral tuberosity.
• Teres tubercle is absent.
• The condyles are of equal size.
• The coronoid fossa is prominent.
• The olecranon fossa is narrow and deep.
• Occasionally the suprtrochlear foramen is found.

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Dog

• The musculospiral groove is shallow.
• The deltoid tuberosity is in the form of a low ridge.
• The lateral tuberosity is undivided.
• The coronoid and the olecranon fossa communicate with each other through the supratrochlear foramen through which no soft structure passes.

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Rabbit

• The head is globose.
• In the distal extremity, the articular surface is double and is separated by a ridge.

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Fowl

• The bone is directed parallel to thoracic vertebrae when the wing is at rest.
• The proximal extremity presents on the medial aspect, an opening leading into the air cavity in its shaft.  

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