Veterinary Dog Anatomy

Note: All the notes provided us from gcvs 

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

Lecture no 3

BONES OF THE THORACIC LIMB(continued)

Veterinary Anatomy  GCVS 1st semester

Radius/Ulna

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.

Ulna

The ulna is located in the caudal part of

the forearm. It exceeds the radius in length and

is irregular in shape and generally tapers from

its proximal to its distal end. Proximally the ulna

is medial to the radius and articulates with the

trochlea of the humerus by the trochlear notch

and with the articular circumference of the radius

by the radial notch.This forms the elbow. Distally

the ulna is lateral and articulates with the radius

medially and with the ulnar and accessory carpal

bones distally.

The proximal extremity is the olecranon,which

includes the olecranon tuber and the anconeal

process. It serves as a lever arm for the extensor

muscles of the elbow. It is four sided, laterally

compressed, and medially inclined. Its proximal

end, the olecranon tuber,is grooved cranially and

enlarged and rounded caudally. The triceps bra-chii, anconeus, and tensor fasciae antebrachii at-tach to the caudal part of the olecranon. The ulnar

portions of the flexor carpi ulnaris and deep digi-tal flexor arise from its medial surface.

The trochlear notchis a smooth, vertical, half-moon–shaped concavity facing cranially. The

whole trochlear notch articulates with the trochlea

of the humerus. At its proximal end a sharp-edged,

slightly hooked anconeal processfits into the olec-ranon fossa of the humerus when the elbow joint

is extended. At the distal end of the notch are the

medialand lateral coronoid processes,which ar-ticulate with the humerus and radius. The medial

coronoid process is larger. Between these processes

is the radial notch for articulation with the articu-lar circumference of the radius.

The bodyof the ulna is three sided in its middle

third; proximal to this the bone is compressed lat-erally, whereas the distal third gradually loses its

borders, becomes irregular, and is continued by

the pointed distal extremity. The ulnar tuberosity

is a small, elongated eminence on the medial sur-face of the bone at its proximal end, just distal tothe medial coronoid process. The biceps brachiiand the brachialis insert on this eminence. The in-terosseous borderis distinct, rough, and irregu-lar, especially at the junction of the proximal and

middle thirds of the bone, where a large, expan-sive, but low eminence is found. This eminence

indicates the place of articulation with the ra-dius by means of a heavy ligament. Frequently,

a vascular groove medial to the crest marks the

position of the caudal interosseous artery. This

groove is most conspicuous in the middle third

of the ulna. The body shows a distinct caudal

concavity.

The distal extremity of the ulna is the head with

its prominent styloid process.A part of this pro-cess articulates with the ulnar and accessory car-pal bones. The head articulates medially with the

radius.

Posted in: 1st semester