THE CPwANIAL NEKVES. 491 



While passing through the jugular foramen, the spinal accessory 

 becomes adherent to the jugular ganglion of the pneumogastric, but 

 without taking part in its formation, except by furnishing one or two 

 small filaments of communication. Immediately after its exit from the 

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

 or anastomotic branch, which joins the trunk of the pneumogastric, 

 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 observers (Bernard, Cruveilhier, Henle, 

 Longet) the internal or anastomotic branch is made up of fibres 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 Bernard and Longet, mechanical or galvanic irritation applied, within 

 the cranium, to the central extremity of the divided nerve, causes no 

 indication of sensibility. On the other hand its fibres may be traced 

 in great part directly to their termination in muscular tissues, and its 

 division or evulsion induces effects which consist exclusively in the loss 

 of motive power. 



The most complete method of experimenting on this nerve is that 

 adopted by Bernard, namely, its evulsion. For this purpose, the mus- 

 cular branch of the nerve is followed by dissection to its point of 

 emergence from the jugular canal, where it separates from the anas- 

 tomotic branch. The combined trunk is then seized between the 

 blades of a forceps, and by steady and continuous traction the whole 

 nerve, with its medullary and spinal roots, may be extracted entire. By 

 appropriate variations of the procedure, either the medullary portion 

 with the anastomatic branch, or the cervical portion with the external 

 branch, may be removed separately, and the comparative effects of the 

 two operations observed. But when the whole trunk is extracted as 

 above, all its fibres, both anastomotic and muscular, are destroyed at 

 the same time. 



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

 of the internal or anastomotic branch. From this branch the pneu- 

 mogastric nerve receives a large share of its motor fibres. According 

 to Cruveilhier, the pharyngeal filament is sometimes given off exclu- 

 sively from the anastomotic branch of the spinal accessory, sometimes 

 partly from this branch and partly from the pneumogastric. Beyond 

 this point, the fibres of the pneumogastric nerve derived from the spinal 

 accessory can no longer be followed by dissection ; but the results of 

 experiment show that they are finally distributed, through the inferior 

 laryngeal branch, to the muscles of the larynx, where they preside over 

 its action as a vocal organ. 



After evulsion of the spinal accessory nerve on both sides, the most 

 noticeable result is loss of power to produce vocal sounds. The respi- 

 ratory movements of the glottis are not interfered with ; but the voice 

 is completely lost, as much so as if the inferior laryngeal nerves, or 



