1896. ] ANATOMY OF PETROGALE XANTHOPUS. 709 
the layers of the adductors and flexores breves to supply these as 
well as the interosseous muscles. 
The internal anterior thoracic nerve is not nearly as large as it 
is in animals with a better developed panniculus: it rises by two 
roots from the 8th cervical and 1st thoracic nerves respectively ; 
these roots unite and supply the posterior and deep parts of the 
pectoral mass as well as the ventro-lateral panniculus. 
The musculo-spiral nerve is formed by the union of two branches 
in front of the teres major muscle; the upper of these comes from 
the 5th, 6th, and 7th cervical, the lower from the union of the 8th 
cervical and 1st thoracic nerves. The musculo-spiral winds round 
the back of the humerus, giving, off branches to the triceps and 
dorso-epitrochlearis as well as a descending branch to the anconeus, 
but no filament to the brachialis anticus or cutaneous twigs. In 
front of the external supracondylar ridge a branch to the supinator 
longus is given off, after which the nerve passes deep to the 
supinator brevis and supplies all the muscles of the back of the 
forearm, as well as a cutaneous branch to the skin of that region. 
The circumflex nerve is given off from the upper branch of the 
musculo-spiral and so can only obtain fibres from the 5th, 6th, 
and 7th cervical nerves; it accompanies the circumflex artery 
through the quadrilateral space, giving off branches to the teres 
minor and shoulder-joint ; it then gives off a large branch to the 
skin of the outer side of the arm and finally supplies the three 
parts of the deltoid. 
The phrenic nerve comes from the junction of the 5th and 6th 
cervicals, and runs back ventral to the plexus and subclavian 
artery, to pursue its usual course through the thorax to the 
diaphragm. 
The posterior thoracic nerve cannot be seen in the axilla until 
just before its distribution ; it rises from the 4th and 5th cervicals, 
and runs back in the substance of the scalenus longus to the 
serratus magnus. 
No intercosto-humeral nerve was seen. 
In studying the foregoing nerves the arrangement of the radial 
is worthy of special attention, because it is opposed to the law 
laid down by Paterson in his most interesting paper on the limb 
plexuses of Mammals’. In that paper the following passage 
occurs :—“ In the case of the fore limb the nerves of distribution 
are derived from the inferior primary divisions of the hinder 
cervical and first thoracic nerves. The nerves entering the plexus 
divide into ventral and dorsal parts, the ventral divisions of the 
nerves combining to form one set, the dorsal divisions combining 
to form another set of nerves of distribution. In no case do 
ventral divisions ever combine with dorsal divisions of adjacent 
nerves. In no case does a nerve of distribution derived in one 
animal from ventral divisions, in another spring from dorsal 
divisions and vice versa.” The musculo-spiral is rightly described 
t Journ. Anat. vol. xxi. p. 622. 
