282 ANATOMY OF THE DOMESTIC FOWL 



vate the levator muscles, and the ventral branches the depressor 

 muscles. 



There is thus given off, throughout the vertebral column, a pair 

 of nerves between each two vertebral segments, making as many 

 pairs of nerves for the region as there are vertebral segments of 

 that region. 



Tlie Brachial Plexus. — The brachial plexus (Fig. 73, No. 19) 

 arises principally from the roots of the last three cervical and the 

 first dorsal spinal nerves. These branches anastomose beneath the 

 deep face of the scapulo-humeral articulation. 



The brachial plexus divides into two distinct parts. The first 

 (Fig. 73, No. 20) the dorsal called the superior thoracic is distributed 

 to the serratus and the rhomboideus muscle. The second is the 

 inferior thoracic (Fig. 73, No. 21), which consists of the main plexus, 

 and which gives off muscular branches especially to the stemo-cora- 

 coideus and to the main portion passing on as the nerve trunk to 

 the structures of the wing. 



From the superior thoracic plexus there are several secondary,, 

 plexuses formed. 



The dorsalis or serratits plexus. This plexus is located adjacent 

 to the anterior part of the main plexus and is formed of from two 

 to four spinal nerve branches. The rhomboideus is supplied by 

 branches which may be traced to the first root of this plexus. 

 This nerve is called the rhomboideus superficiahs. Another nerve 

 is given off from the middle part of the dorsal side of the plexus 

 and is called the rhomboideus profundus. A third, the superficiahs 

 serratus, is the largest of the branches. It breaks up into terminal 

 branches, one going to each serration, or digitation, of the serratus 

 muscle. Branches from the anterior portion of this plexus are dis- 

 tributed to the patagii muscles. 



The superior brachial plexus- gives off the following nerves: 



The subcoraco-scapularis, which is purely a motor nerve, springs 

 from the anterior roots of the plexus. It gives off a branch to the 

 following three muscles: subcoracoideus, subcoracoido-scapularis, 

 a,nd scapulo-humeralis. 



The scapulo-humeralis is distributed to the scapular humeral 

 region. 



The latissimus dor si is located on the peripheral border of the scap- 

 ulo-humerahs or supra-spinatus. It originates from the second, 

 and the fourth nerve roots of the plexus.- It is located on the dorsal 



