Human anatomy, including structure and development and practical considerations . fibres arise from neuroblasts situated in the dorsal part of the ventral zone of the wall ofthe hind-brain just posterior to the otic vesicle. The sensory part of the nerve, along withthat of the vagus, offers greater , since it is developed, as shown by Streeter ^, fromtwo sources. The ganglion of the root (g. superius or jugular ganglion) arises very early asa small mass of cells derived from the ganglion-crest of the hind-brain. It varies in size andsoon ceases to grow, which behavior, in connection
Human anatomy, including structure and development and practical considerations . fibres arise from neuroblasts situated in the dorsal part of the ventral zone of the wall ofthe hind-brain just posterior to the otic vesicle. The sensory part of the nerve, along withthat of the vagus, offers greater , since it is developed, as shown by Streeter ^, fromtwo sources. The ganglion of the root (g. superius or jugular ganglion) arises very early asa small mass of cells derived from the ganglion-crest of the hind-brain. It varies in size andsoon ceases to grow, which behavior, in connection with the preponderating ingrowth of themotor fibres, accounts for the well-known inconstancy of the structure. The ganglion ofthe tnmk (g. petrosum) arises, according to Streeter, not from the neural crest, but inrelation with the ectoblast of the second visceral furrow. At first ununited with the smallerganglion superius, the ganglion of the root subsequently becomes joined to it, the two nodes ^ Amer. Jour, of Anatomy, vol. vi., 1907.^Amer. Jour, of Anatomy, vol. iv., Sympathetic \agus Reconstruction of peripheral nerves of human embryo of five weeks(14 mm.) / ij. [Streeter.) 1380 HUMAN ANATOMY. being later closely related, both as to position and fibres. An outgrowth of distally directeafibres establishes the main trunk of the ner\e, while a forwardly growing strand represents thelater tympanic branch. The vagus and spinal accessory nerves are so inseparably related in their developmentthat their origin must be regarded as proceeding from a common vagus complex. The lattercomjirises three elements: (<?) a series of motor roots, which arise from the ventral zone ofthe hind-brain and extend from near the glosso-i)haryngeal anlage in front as far as the third orfourth spinal segment below ; (/;) a partially subdivided, but at first continuous, ganglionicmass, which arises from the ganglion-crest of the hind-brain and represents the root-ganglia;(r) a secondary ventra
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