Veterinary Anatomy

Note: All the notes provided us from gcvs 

recomended book Guide To The Dissection Of Dog By Howard E. Evans, PhD 

Lecture no 2

BONES OF THE THORACIC LIMB(continued)

Veterinary Anatomy  GCVS 1st semester

Humerus

The humerus is located in the arm, or

brachium. This bone enters into the formation of

both the shoulder joint and the elbow joint. The

shoulder joint is formed by the articulation of the

scapula and humerus; the elbow joint is formed

by the articulation of the radius and ulna with

each other and with the humerus. The proximal

extremity of the humerus includes the head, neck,

and the greater and lesser tubercles. The distal ex-tremity, the condyle, includes the trochlea, capitu-lum, and the radial and olecranon fossae, which

communicate proximal to the trochlea through the

supratrochlear foramen. The medial and lateral

epicondyles are situated on the sides of the con-dyle. The body of the humerus lies between the

two extremities.

The headof the humerus is the part that articu-ates with the scapula. It presents more than twice

the area of the glenoid cavity of the scapula and

is elongated sagittally. Although the shoulder joint

is a typical ball-and-socket joint, it normally under-goes only flexion and extension. The intertubercu-lar groovebegins at the cranial end of the articular

area. It lodges the tendon of origin of the biceps

brachii and is deflected toward the median plane by

the greater tubercle,which forms the craniolateral

part of the proximal extremity. The greater tubercle

is convex at its summit and, in most breeds, higher

than the head. It is continued distally in the body

of the humerus by the crest of the greater tubercle.

The greater tubercle receives the insertions of the

supraspinatus and the infraspinatus and part of the

deep pectoral. Between the head of the humerus

and the greater tubercle are several foramina

for the transmission of vessels. The infraspinatus is

inserted on the smooth facet on the lateral side of

the greater tubercle. The lesser tuberclelies on the

medial side of the proximal extremity of the hu-merus, caudal to the intertubercular groove. It is

not as high or as large as the greater tubercle. The

subscapularis attaches to its proximal border. The

neckof the humerus is not distinct except caudally.

It is the line along which the head and parts of the

tubercles have fused with the body.

The cranial surfaceof the humerus is distinct

in the middle third of the body, where it furnishes

attachment for the brachiocephalicus and part of

the pectorals. Distally it fades but may be consid-ered to continue to the medial lip of the trochlea.

On the proximal third of the cranial border are

two ridges. They continue to the cranial and cau-dal parts of the greater tubercle. The ridge that ex-tends proximally in a craniomedial direction is the

crest of the greater tubercleand is also the cranial

border of the bone. This forms part of the area of

insertion of the pectorals and the cleidobrachialis.

The ridge extending to the caudal part of the

greater tubercle is on the lateral surfaceof the hu-merus. Distally it is thickened to form the deltoid

tuberosity.The deltoideus inserts here. From this

tuberosity to the caudal part of the greater tubercle,

the ridge forms the prominent tricipital line. The

lateral head of the triceps arises from this line. The

teres minor inserts on the tuberosity of the teres

minoradjacent to the proximal extremity of the tri-cipital line. The smooth brachialis grooveis on the

lateral surface of the body. The brachialis, which

originates in the proximal part of the groove, spirals

around the bone in the groove so that distally it lies

on the craniolateral surface. Distal to this groove is

the thick lateral supracondylar crest.The extensor

carpi radialis and part of the anconeus attach here.

The crest extends distally to the lateral epicondyle.

The caudal surfaceis smooth and rounded trans-versely and ends in the deep olecranon fossa.

The crest of the lesser tuberclecrosses the prox-imal end of the medial surfaceand ends distally at

the teres major tuberosity.The teres major and la-tissimus dorsi are inserted on this tuberosity. Cau-dal and proximal to this, the medial head of the

triceps arises and the coracobrachialis is inserted.

Approximately the middle third of the medial sur-face is free of muscular attachment and is smooth.

The distal end of the humerus, including its ar-ticular areas and the adjacent fossae, is the humeral

condyle.The articular surface is divided unevenly

by a low ridge. The large area medial to the ridge

is the trochlea,which articulates with both the ra-dius and the ulna and extends proximally into the

adjacent fossae. The articulation with the trochlear

notch of the ulna is one of the most stable hinge

joints (ginglymus) in the body. The small articular

area lateral to the ridge is the capitulum,which

articulates only with the head of the radius.

The lateral epicondyleis smaller than the me-dial one and occupies the enlarged distolateral

end of the humerus proximal to the capitulum. It

gives origin to the common digital extensor, lateral

digital extensor, ulnaris lateralis, and supinator.

The lateral collateral ligament of the elbow also

attaches here. The lateral supracondylar crest ex-tends proximally from this epicondyle and is the

origin for the extensor carpi radialis.

The medial epicondyleis the enlarged disto-medial end of the humerus proximal to the trochlea.

Its caudal projection deepens the olecranon fossa.

The anconeus arises from this projection. The ele-vated portion of the medial epicondyle serves as

origin for flexor carpi radialis, flexor carpi ulnaris,

pronator teres, and the superficial and deep digital

flexor muscles. The medial collateral ligament of

the elbow also attaches here.

The olecranon fossais a deep excavation of the

caudal part of the humeral condyle. It receives the

anconeal process of the ulna during extension of

the elbow. On the cranial surface of the humeral

condyle is the radial fossa,which communicates

with the olecranon fossa by an opening, the supra-trochlear foramen.No soft structures pass through

this foramen.

Radius

The radius and ulna are the bones of the antebra-chium, or forearm. It is important to know that

they cross each other obliquely so that the proxi-mal end of the ulna is medial and the distal end

is lateral to the radius. The radius (Fig. 2-6), the

shorter of the two bones of the forearm, articulates

proximally with the humerus and distally with the

carpus. It also articulates with the ulna, proximal-ly by its caudal surface and distally near its lateral

border.

The proximal extremity consists of head, neck,

and tuberosity. The headof the radius, like the

whole bone, is widest medial to lateral. It forms

proximally an oval, depressed articular surface,

the fovea capitis,which articulates with the

capitulum of the humerus. The smooth caudal

border of the head is the articular circumfer-encefor articulation with the radial notch of the

ulna. The small radial tuberositylies distal to

the neck on the medial border of the bone. The

biceps brachii and brachialis insert in part on

this tubercle.

Head

Capitular fovea

Articular

circumference

Radial tuberosity

Medial border

Trochlea

Styloid process

Articular face

Ulnar notch

Lateral border

Neck

Left radius, caudal view.

Guide to the Dissection of the Dog 12

The bodyof the radius is compressed so that it

possesses cranial and caudal surfaces and medial

and lateral borders. It is slightly convex cranially.

At the carpal end, the body blends without sharp

demarcation with the enlarged distal extremity.

The caudal surface of the radius is roughened and

slightly concave. It has a ligamentous attachment

to the ulna. Distally it broadens and becomes the

expanded caudal surface of the distal extremity.

The cranial surface of the radius, convex trans-versely, is relatively smooth throughout.

The distal extremity of the radius is the troch-lea.Its carpal articular surface is concave. On the

lateral surface of the distal extremity is the ulnar

notch,a slightly concave area with a facet for ar-ticulation with the ulna. The medial surface of the

distal extremity ends in a rounded projection, the

styloid process.The medial collateral ligament of

the carpus attaches proximal to the styloid process.

The cranial surface of the distal extremity presents

three distinct grooves. The most medial groove,

which is small, short, and oblique, contains the

tendon of the abductor digiti I longus. The middle

and longest groove, extending proximally on the

shaft of the radius, is for the extensor carpi radi-alis. The most lateral of the grooves on this surface

is wide and of variable distinctness. It contains the

tendon of the common digital extensor.

Posted in: 1st semester