IX. The ninth and tenth nerves are the largest of the brachial plexus. The former, after giving off some twigs to the ventral musculature and to the serratus superficialis and the hinder regions of the collo-thoraci-suprascapularis profundus muscles, unites with the tenth nerve just after giving off the small thoracicus inferior nerve to the costo-coracoideus muscle. After uniting with the tenth nerve the ninth nerve immediately divides into two branches that form loops with branches of the eighth nerve, the whole making a very complicated plexus. X. The tenth nerve, as noted above, is one of the two largest nerves of the brachial plexus. After giving off a single nerve to the ventral musculature, this nerve unites with the eleventh nerve; it then gives a branch to the costo-coracoideus muscle and forms a loop with the ninth nerve. After giving off a couple of nerves it again divides into two equal branches which unite with similar branches of the eighth nerve. XI. The eleventh nerve is next to the smallest of the plexus. Besides branches to the trunk musculature it gives a fine twig to the integument of the axilla and unites with the tenth nerve in the brachial plexus. This is the last nerve that enters into the brachial plexus. [Illustration: FIG. 31. BRACHIAL PLEXUS OF C. ACUTUS. (From Bronn, after Fürbringer.) VII-XI. ventral branches of seventh to eleventh spinal nerves. 3_a_. thoracicus anterior VII. 4. thoracicus superior V. 7. thoracicus superior VI. 7_a_. proximally-leading thoracicus superior. 7_b_. distally-leading thoracicus superior VIII. 9. thoracicus superior IX. 10_a_, 10_a₁_, 10_a₂_, 10_a₃_. thoracicus inferior. 18. cutaneus pectoralis. 19. pectoralis. 21. brachialis longus inferior. 22. coraco-brachialis. 22_c_. branch for the distal belly of biceps muscle. 24. muscular branch for the humero-antebrachialis inferior. (25 + 42). cutaneus brachii and antebrachii medialis. 29. subscapularis. 31. dorsalis scapulæ (posterior). 32. cutaneus brachii superior lateralis. 33. deltoides inferior. 34. brachialis longus superior. 36. anconæus. 36_a_. scapulo-humeralis profundus.]