Humerus | Gross Anatomy | Anjani Mishra

The HUMERUS

Written By Anjani Mishra

Shape: It is long cylindrical bone.

Location: proximal end of the forelimb.

Direction : Obliquely downwards and backwards.

Relation: It articulated with the scapula above and radius -ulna below. It forms shoulder joint above with the scapula and elbow joint below radius & ulna.

Composition: Consists of a shaft and two extremities .

1. Shaft : It is twisted, cylindrical and presents four surfaces .

    A. Anterior Surface: it is triangular , wide and smooth above and narrow below. It bears             muscular imprints in its middle and distal parts.

    B. Posterior Surface: It is rounded and smooth , and blends with the lateral surface .Nutrient Foramen is present at middle of the distal –third of this surface.

    C. Medial Surface : It is rounded, nearly straight and blends with the anterior and posterior surfaces. At the middle, the teres tubercle is present for the insertion of the teres major  m/s  n

    D. Lateral Surface: It has musculo-spiral groove which lodges the brachialis m/s . lateral surface is separated from the anterior surface by a distinct border, the deltoid ridge, which ends distally above the coronoid fossa. At the middle of the ridge, there is a prominence for the insertion of deltoid m/s, termed as Deltoid tuberosity . Extending from this deltoid tuberosity to the articular head, is a curved line to which the triceps m/s is attached.  Immediately behind  this curved line, placed on the extreme dorsal surface, is a nodule for the insertion of teres minor m/s.

 2. Extremities: Two

A. Proximal Extremity: It is voluminous part of bone and is composed of on articular head, two tuberosities and a bicipital groove.

i) Head: It is placed behind and is large, rounded, convex and double the size of the glenoid cavity of the scapula. Neck is the constricted part just below the head. 

ii) Tuberosity: Two: Lateral and Medial tuberosity separated by inter-tuberal groove.

a.       Lateral tuberosity : Large, prominent and rises above the head. It is situated on the antero- external part of the head and is divided into summit and a convexity. The summit forms the outer boundary of the bicipital groove and overhangs it. Below and external to the summit is a large, circular rough area, for the insertion of the infraspinatus m/s. The summit is attached to the lateral tendon of the supraspinatus m/s.

b.       Medial tuberosity : It is much small and is divided into two parts: anterior and posterior.

• Anterior Medial Tuberosity: It forms the medial boundary of the bicipital groove and curves over it. Its gives attachment to the medial tendon of the supraspinatus above and to the deep pectoral m/s below.
• Posterior Medial Tuberosity : it gives attachment to the sub-scapularis m/s.
•  Bicipital groove (inter-tuberal groove) : it is situated on the anterior part of the proximal extremity and is bounded by the anterior parts of the two tuberosities. The bicipital groove gives passage to the tendon of the biceps brachii m/s.

b. Distal Extremity: It is articular and is divided into two condyles: Medial (Trochlea) and Lateral (Capitulum) condyle, by an antero-posterior ridge. 

•   This end also consist medial and lateral epicondyle, olecranon fossa and the radial/ coronoid fossa.
•    The medial condyle is much larger than lateral and is transversed by an antero-posterior deep groove, which reaches the olecranon fossa. This extension articulates with the semilunar notch of the ulna posteriorly.
•    The lateral condyle is much smaller and is placed lower, which gives this extremity an oblique appearance. Anteriorly, above the articular area is a depression, the coronoid fossa, which receives the coronoid process of the radius during extreme flexion of the joint. Posteriorly, above the articular area, is much deeper oleranon fossa, which receives the olecranon process of the ulna during extreme extension of the joint if bounded on either side by a prominent ridge, the epicondyle.

•          The medial epicondyle gives origin to the flexor carpi radialis, pronator teres, flexor carpi ulnaris, superficial digital flexor and the humeral head of the deep digital flexor.
•           The lateral epicondyle gives origin to the ulnaris lateralis at its tuberous portion. Lateral epicondyle marks on its lateral aspect, the condyloid crest which forms posterior boundary of the musculo-spiral groove and gives origin to the extensor carpi radialis, common digital extensor and medial digital extensor m/s.

Comparative anatomy of humerus: 

A) Horse:

• Musculo-spiral groove is deeper and is more spirally curved.
• Nutrient foramen is placed on the distal-third of the medial surface.
• Deltoid tuberosity is better developed.
• Head is smaller, neck id less distinct.
• The bicipital groove is again divided by an intermediate ridge.
• Summit of the lateral tuberosity is not high and arched inwards.
• The ridge on the distal articular surface is less prominent. 

 

b) Pig :

• Both proximal and distal ends are inclined.
• Musculo-spiral groove is shallow.
• Supratrochlear foramen may be present.

c) Dog:

• Humerus is relatively long and slender, but is less spirally twisted.
• The deltoid tubersoity is ridge like.
• The teres tubercle is a raised rough area.
• The nutrient foramen is placed on the posterior surface.
• Head is rounded and strongly convex, the lateral tuberosity is single while the bicipital groove is undivided.
• The coronoid and olecranon fossa usually communicate by a large foramen (supratrochlear foramen).

d) Rabbit:

• Head is elongated.
• Deltoid tuberosity is in the form of a ridge.
• Musculo-spiral groove is shallow.
• Supra-trochlear foramen is present.

e) Fowl:

• Proximally, this bone articulates with scapula and coracoid.
• The pneumatic foramen is situated medially below the head.
• The body is less twisted.
• The head is oval in form.

 

If you have any questions you can ask me on :
mishravetanatomy@gmail.com 

Facebook Veterinary group link -  https://www.facebook.com/groups/1287264324797711/ 

Twitter - @MishraVet
Facebook - Anjani Mishra

Website: mishravetanatomy.blogspot.com