1896.] ANATOMY OF rETBOGALH XANTIIOPUS. 709 



tlie layers of (he 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 pariniculus : 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 5tb, 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 ofE branches to the triceps and 

 dorso-epitrocblearis 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, Cth, 

 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 



' Journ. Aiiat. Vol. xxi. p. 622. 



