THE LIMBS OF THE HORSE 7 



Dissection. — It will facilitate the examination of the brachial plexus of 

 nerves if the axillary vein and artery are cut across close to the first rib. 



In cleaning the brachial plexus the dissector will be well advised to 

 work solely from the trunk towards the limb. This will diminish the 

 chance of a false division of nerves. 



Plexus brachialis. — The brachial plexus ^ is the broad band of 

 nerves that appears between the two parts of the scalenus muscle, 

 and is formed by the ventral divisions of the sixth, seventh, and eighth 

 cervical, and the first and second thoracic nerves. The seventh and 

 eighth cervical and the first thoracic contribute most to the plexus; 

 only comparatively slender contributions are furnished by the sixth 

 cervical and second thoracic nerves. 



From the narrow interval between the two portions of the scalenus 

 muscle, where its caudal border is in contact with the first rib, the 

 plexus sweeps in a caudal and ventral direction into the axilla and divides 



9 



into the following branches : — Suprascapular, subscapular, musculo- 

 cutaneous, axillary, radial, median, ulnar, thoracodorsal, pectoral, and 

 long thoracic nerves. 



With the exception of the three last-named, these nerves are 

 distributed to the limb. At the present time it will suffice to identify 

 them and leave their fuller examination until later. 



'IsT. THOEACODOESALis. — The thoracodorsal nerve pursues an oblique 

 course across the medial face of the scapular region, and ends in the 

 latissimus dorsi muscle. 



IsTn. pectoeales. — The pectoral nerves may be divided into two 

 groups: — (1) The cranial nerves (nn. pectorales craniales) are three 

 or four in number, and supply the cranial part of the pectoral mass of 

 muscles as well as a part of the brachiocephalic muscle. (2) A caudal 

 pectoral nerve (n. pectoralis caudalis) furnishes twigs to the remainder 

 of the pectoral mass and the cutaneous muscle. It has already been 

 seen in company with the external thoracic vein at the border of the 

 deep pectoral muscle. 



N. THOEACALIS LONGUS. — The long thoracic nerve is somewhat 

 isolated from the rest of the branches of the brachial plexus, inasmuch 

 as it clings closely to the surface of the ventral serratus muscle, of 

 which it is the nerve of supply. 



M. SEEEATUS VENTEALis. — The extensive ventral serratus ^ muscle 

 may be regarded as taking origin from the rough triangular 

 areas on the costal surface of the scapula and the adjoining part 

 of the scapular cartilage. From this _ origin the fibres diverge, with 

 the result that the muscle has a triangular or fanlike outline. The 



1 Plexus [L.], plaiting, ivomplecto, to plait, braid, or interweave. 



2 Serratus [L.], s©rg?fl'2@tf i^yrmf^rSmft®''"' ^ saw. 



