Comparative anatomy of M. extensor carpi radialis in 9 species of

ARTICLE ORIGINAL
Comparative anatomy of M. extensor carpi
radialis in 9 species of domestic Mammals
and in Man
C. GUINTARD and F. COSSU
École Nationale Vétérinaire de Nantes, Unité d’Anatomie Comparée, route de Gachet, B.P. 40706, F-44307 Nantes Cedex 03
Correspondant : Dr. C. Guintard, ENVN, Tél. : 02 40 68 77 35, Fax : 02 40 68 77 62, E-mail : [email protected]
SUMMARY
RÉSUMÉ
As a sequel to the study published by COSSU and GUINTARD [7], this
research work compares the morphology of M. extensor carpi radialis in
Man and in 9 species of domestic Mammals (sheep/cats/dogs/rabbits/oxen/
horses/pigs/mice and rats). Separation into 3 broad morphological types is
suggested as a way to simplify the overall plan which goes from two distinct muscles to a single one in line with a loss of the movements of pronation and supination.
Anatomie comparée du muscle extenseur radial du carpe (M. extensor
carpi radialis) chez 9 espèces de Mammifères domestiques et chez
l’Homme. Par C. GUINTARD et F. COSSU.
Faisant suite à l’étude publiée par COSSU et GUINTARD [7], ce travail
de recherche compare la morphologie du muscle extenseur radial du carpe
chez l’Homme et 9 espèces de Mammifères domestiques (Mouton, Chat,
Chien, Lapin, Bœuf, Cheval, Porc, Souris et Rat). La séparation en trois
grands types morphologiques est suggérée comme étant une voie de simplification d’un plan d’organisation général qui va de deux muscles distincts à
un seul muscle, en relation avec la perte des mouvements de pronation et de
supination.
KEY-WORDS : comparative anatomy - M. extensor carpi
radialis - domestic Mammals - Man.
MOTS-CLÉS : anatomie comparée - M. extenseur radial
du carpe - Mammifères domestiques - Homme.
Introduction
Materials and methods
The descriptive anatomical study of M. extensor carpi
radialis, in the main species of domestic Mammals, has
enabled us to differentiate between 3 broad morphological
types [7]. In Man, we note the association of a M. extensor
carpi radialis longus combined with a M. extensor carpi
radialis brevis [12, 14] ; on the other hand, in sheep, there is
a single muscle [2, 7]. At an intermediate stages, within some
Carnivores and Lagomorphs, we note a more or less clear
division of the fleshy part, which is prolonged by a double
tendon [3, 5]. This work aims at furthering the study published in 2000, as it involves a greater number of species of
domestic Mammals, so as to offer a typology based on the
morphology of the muscle, its irrigation and innervation in
relation to phenomena connected with adaptation.
The initial study [7] involved 5 species (Man, Cat, Dog,
Rabbit and Sheep). It has been completed by 5 others species :
Rat, Mouse, Pig, Cattle and Horse. The dissections were carried out on previously deep frozen animals from the autopsy
department of the Nantes Veterinary school. We worked on
4 thoracic limbs of rats, 4 thoracic limbs of mice, 6 thoracic
limbs of pigs, 4 thoracic limbs of bovines and 4 thoracic
limbs of horses. This sample completed the initial group
which comprised 6 human thoracic limbs, 4 from rabbits,
6 from cats, 4 from dogs and 2 from sheep. In each dissection, we have described the attachments of M. extensor carpi
radialis, its interactions, its innervation and its blood supply.
Liquid latex was injected into the arterial system, hardened
by 24 hours in a deep freeze. The injection was made into a.
axillaris.
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GUINTARD (C.) AND COSSU (F.)
Results
M. EXTENSOR CARPI RADIALIS IN RATS AND MICE
(Fig 2)
M. extensor carpi radialis runs along the cranial surface of
the radius. It is a prismatic muscle which ends with a double
tendon. It is attached at the level of the lateral epicondyle of
the humerus, runs along at the level of the elbow crease and
medially, is attached on the II and III metacarpial [10, 13]. On
its lateral surface lies the m. extensor d i g i t o rum communis.
m. extensor carpi radialis is crossed on its cranial side by the
fleshy part of the m. extensor carpi obliquus at the distal end
of the radius. On its surface, it is covered by the v. cephalica
antebrachii and the adjacent nerve branches. Blood is supplied by a collateral branch of the a. brachialis : a. transversa
cubiti, which merges with the a. collateralis radialis by the
recurrent radial artery. In the area of the elbow crease, its
innervation is achieved through fine branches of the n. radia lis.
In both species, removing the perimysium covering of the
muscle, makes it possible to divide the fleshy part into two
(in the proximal 1/3). Each part ends in a single tendon.
M. EXTENSOR CARPI RADIALIS IN PIG, HORSE AND
CATTLE (Fig 2)
M. extensor carpi radialis is the largest of the extensor
muscles in the forearm [1, 2, 4, 6, 7, 15]. It is a muscle with a
fleshy part, oval in shape, which ends in a single tendon. It is
originates at the level of the lateral humeral epicondyle and
inserts distally on the dorsal and proximal sides of the main
metacarpal (respectively the third metacarpal in horse, the
third and fourth in cattle and pig).
On its lateral side, it touches the m. extensor d i g i t o ru m
communis. The blood supply of the fleshy part is provided by
the a. tranversa cubiti, collateral of the a. brachialis.
Innervation is achieved through a main nerve branch of n.
radialis. The fleshy part cannot be divided and when it is
removed from its covering the tendon remains single.
Discussion
The anatomical study of the m. extensor carpi radialis in
the five other species previously studied enabled us to clarify
the morphological evolution of the muscle within animal
groups, particulary within the main domestic Mammals, in
comparison with Man [8, 9].
As a result we noted :
- the human type :
The presence of the m. extensor carpi radialis longus and
the m. extensor carpi radialis brevis,
Innervation comes from n. radialis,
The blood supply comes from a collateral branch of a.
radialis.
- the type seeing in Pig, Sheep, Cow and Horse
A single fleshy part, which is prolonged by a single tendon,
Innervation comes from n. radialis,
a stylopode
b, c zeugopode
1 a. brachialis, 2 a mediana, 3 a. radialis, 4 a. récurrente radiale (BARONE, 1996), 5 a collateralis radialis, 6 a. transversa cubiti (a. radiale proximale
(BARONE, 1996)), 7 a. radialis (a. radiale distale (BARONE, 1996)), 8 a. brachialis superficialis, 9 Aa radiales superficiales, 10 a. antebrachialis superfi ciellis cranialis, 11 a. radialis proximalis (a. radiale proximale (BARONE, 1996).
FIG. 1. — Radial arterial system of the forearm in Man (A), Horse (B), Dog and Cat (C), Pig (D) and Cattle (E).
Revue Méd. Vét., 2003, 154, 2, 115-119
COMPARATIVE ANATOMY OF M. EXTENSOR CARPI RADIALIS IN 9 SPECIES OF DOMESTIC MAMMALS AND IN MAN
* anastomosis between the transversal cubital artery and the radial collateral artery
_ radial system
TABLE I. — Nomenclature of the radial arterial system of the forearm according to the NA/NAV, the English translation and the terms used by R. BARONE(1996).
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118
Blood supply comes from a collateral branch of a. bra chialis.
- an intermediate type as seen in Cat and Rabbit
Two fleshy parts ending in a single tendon,
- an intermediate type as seen in Dog, Rat and Mouse
The fleshy part divides at the level of the two distal thirds
and ends in two tendons
Innervation comes from n. radialis,
The blood supply comes from a collateral branch of a. bra chialis.
So, the division of the fleshy part of the m. extensor carpi
radialis seems to become simpler in those species which
have lost pronation and supination. Curiously, the cat and the
rabbit show a similar type of extensor carpi radialis muscle
(muscle body divided, a single tendon), considering prosupination movements have completely disappeared in the latter,
and remain prominent in the former.
When there are no longer two muscles but a single one, one
notes that there is a substantial simplification of the blood
supply system (Table I, Fig 1). Thus the radial system which,
in Man, is one of the two branches stemming from a. bra chialis, no longer exists in the other species except in the
shape of collaterals coming from a. brachialis and a.
mediana. When BARONE [3, 4] describes this arterial supply in Man and the domestic Mammals, he uses the term of
proximal radial artery in lieu of the a. transversa cubiti.
One should not forget that this artery which in animals is a
collateral of a. brachialis is, in Man, a collateral of a.
mediana.
To call the artery which irrigates the carpus area in the different animal species studied, radial artery is a misnamer. In
fact, in these species, this artery represents the distal part of
the radial artery in Man. Apparently, the homologue of the
radial artery in Man is the transversal cubital artery in the
others species studied. Indeed, the transversal cubital artery
irrigates the muscle in the cranial area of the forearm, near
the radius.
Nevertheless, in comparison to Man, the radial arterial system of the forearm regresses in association with the loss of
the supination movement in the other species. This regression is illustrated in Figure 1, in which two distinct systems
of irrigation can be distinguished:
- in Man : a well developed radial arterial system
- in the other species : a more or less significant regression
of the radial artery and a subdivision of it.
GUINTARD (C.) AND COSSU (F.)
Conclusion
The adaptation of a species to a certain way of life and
more precisely to a certain type of locomotion brings about
significant morphological variations.
Thus, within the main species of domestic Mammals, the
loss of pronation and supination seems to be associated with
a regression of the associated arterial system.
This study has also enabled us to complete the initial
sample and shows that the suggested typology remains valid
even when it is extended to other species of domestic
Mammals.
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COMPARATIVE ANATOMY OF M. EXTENSOR CARPI RADIALIS IN 9 SPECIES OF DOMESTIC MAMMALS AND IN MAN
a
b
c
d
1 radius, 2 carpus, 3 m. extensor carpi radialis, 4 m. extensor digitorum communis, 5 m. extensor carpi obliquus
FIG. 2. — Dorsal aspect of the forearm in a Rat (a), a Horse (b), a Cow (c) and a Pig (d).
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