572 THE CRANIAL NERVES. 



becomes adherent externally to the jugular ganglion of the pneumogas- 

 tric, but without taking any part in its formation, except by furnishing 

 one or two small filaments of communication. Immediately upon its 

 exit from the foramen it divides into two main branches; namely, 1st, 

 the internal, or anastomotic branch, which joins the trunk of the pneu- 

 mogastric and becomes more or less intimately blended with it, and 

 2dly, the external, or muscular branch, which passes downward and 

 outward and is distributed to the sterno-mastoid and trapezius muscles. 

 According to many different observers (Bernard, Cruveilhier, Henle, 

 Longet) the internal or anastomotic branch is made up of nerve fibres 

 coming from the medulla oblongata ; the external or muscular branch 

 consists of those originating from the spinal cord. 



The spinal accessory is without question a motor nerve. According 

 to the experiments of Longet on dogs, its mechanical irritation in the 

 cranial cavity does not give rise to signs of pain, and although Bernard 

 found evidences of sensibility on galvanizing the uninjured nerve in 

 the same situation, if it were divided and the irritation applied to its 

 central extremity no indications of sensibility were manifest. On the 

 other hand its fibres may be traced in great part directly to their termi- 

 nation in muscular tissues, and its division or evulsion induces effects 

 which consist exclusively in loss of motive power. 



The most complete method of experimenting upon the effects pro- 

 duced by destruction of this nerve is that first adopted by Bernard, 

 namely, its evulsion, For this purpose, the muscular branch of the 

 nerve is followed by dissection from without to its point of emergence 

 from the jugular canal, where it separates from the anastomotic branch. 

 The combined trunk is then seized between the blades of a forceps, and 

 by a steady and continuous traction the whole of the nerve, witli both 

 its medullary and spinal roots, may be separated from their central 

 attachments and extracted entire. By appropriate variations of the pro- 

 cedure, either the medullary portion with the anastomatic branch, or the 

 cervical portion with the external branch, may be taken away separately, 

 and the comparative effects of the two operations observed. But when 

 the entire trunk is extracted as above, the source of the fibres destined 

 both for anastomosis with the pneumogastric, and for the muscular 

 branch of the nerve, is destroyed at the same time. 



The most striking effects of this operation are due to paralysis of the 

 internal or anastomotic branch. It is this branch which supplies to the 

 pneumogastric nerve a large share of its motor fibres ; and those espe- 

 cially which form the pharyngeal branch of the pneumogastric nerve, are 

 shown by dissection to be derived from the anastomotic branch of the 

 spinal accessory. According to Cruveilhier, the pharyngeal filament is 

 sometimes given off exclusively from the anastomotic branch of the 

 spinal accessory, sometimes partly from this branch and partly from the 

 pneumogastric itself. Beyond the pharyngeal branch, the fibres of the 

 pneumogastric nerve derived from the spinal accessory can no longer 

 be followed with certainty by means of dissection ; but the results of 



