6 THE ANATOMY OF THE HORSE. 



III. The root from the 8th cervical nerve gives a branch to the nerve for the serratus 

 magnus, and then sends its fibres in three directions, viz.,— 1. To the before-mentioned 

 flat fasciculus giving off the subscapular, etc. ; 2. to join the cord from which arise the , 

 posterior root of the median, the ulnar, and the subcutaneous thoracic nerve ; 3. to the 

 anterior root of the median and the nerve for the anterior deep pectoral muscle. 



IV. The roots from the 1st and 2nd dorsal nerves unite to form a common cord which 

 divides its fibres in two directions, viz.,— 1. To join the above-mentioned cord giving off 

 the posterior root of the median, etc. ; 2. to join the broad fasciculus from which arise 

 the subscapular, etc. 



The following is a list of the branches of the plexus : — 



1. The phrenic or diaphragmatic nerve (in part). 



2. The suprascapular nerve. 



3. Nerves to the pectoral muscles. 



4. The nerve to the subscapularis. 



5. Nerves to the serratus magnus and levator anguli scapulae 



(cervical portion of the serratus), the latter only in part. 



6. The circumflex nerve. 



7. Nerves to the teres major and latissimus dorsi. 



8. The musculo-spiral nerve. 



9. The median nerve (two roots). 



10. The ulnar nerve. 



11. The subcutaneous thoracic nerve. 



The Phrenic Nerve. This nerve is formed by the union of two, or 

 sometimes three, branches. The inconstant branch comes from the 

 5th cervical ; the other two come from the 6th and 7th respectively. 

 The root from the 6th nerve gives off a branch to the brachial plexus, 

 and then unites on the scalenus with the root from the 5th — when that 

 is present. The single cord resulting passes obliquely backwards and 

 downwards, and at the lower edge of the scalenus it joins with the root 

 from the 7th nerve. This last comes from the fore part of the brachial 

 plexus. The trunk of the nerve, as thus formed, passes backwards 

 between the axillai-y artery and its inferior cervical branch, and enters 

 the thorax. It is the motor nerve to the diaphragm. 



The Nerves to the Levator Anguli SoAPULiE and Rhomboidbus. 

 In Plate 3 two nerves are seen at the upper edge of the scalenus. 

 They are not, sti-ictly speaking, branches of the brachial plexus ; but 

 come from the inferior primary branch of the 6th nerve, and pierce 

 the muscle either together or separately. They are distributed to the 

 levator anguli scapulae, and the posterior of the two is continued in 

 that muscle to reach the rhomboideus. 



The Nerve to the Serratus Magnus is formed by the union of two 

 branches, which pierce the upper division of the scalenus before uniting. 

 These are brandies of the 7th and 8th nerves respectively. By their 

 fusion there is formed a broad nerve, which passes backwards on the 

 surface of the serratus, distributing its filaments upwards and down- 



