THE CRANIAL OE ENCEPHALIC NERVES. 737 



spinal nerve, a fact which is sufficiently indicated by the name generally 

 given to it. 



In the interior of the spinal canal, it is a long cord measuring from 

 27 to 31 inches in middle-sized animals. It commences, by a very fine 

 point, at the cervical or brachio-rachidian bulb of the spinal -cord, follows 

 that organ in an ascending course, lying close to its lateral column, and 

 passing between the roots of the two orders of cervical nerves until it arrives 

 at the medulla oblongata, where it is inflected outwards at the foramen 

 lacerum posterius, into which it passes to leave the cranium. 



In this ascending track, it gradually increases in volume, as it at 

 intervals receives additional filaments from the lateral column of the spinal 

 cord, like the radicular extremity of the nerve itself. Before making its 

 escape from the cranium, it receives, besides, some of the posterior or motor 

 roots of the pneumogastric nerve. In the foramen lacerum, it becomes 

 applied against the ganglion (jugular) of that nerve, in the manner of motor 

 fibres of mixed nerves, and gives it some of its proper filaments. 



The long cord here described as the root of the spinal accessory, is 

 considered by some authorities as only a portion of this nerve, to which 

 they give the name of external or medullary root of the spinal accessory. 

 They designate as the internal or bulbous root of that nerve, the anastomosing 

 filaments already described as the motor roots of the pneumogastric. 

 According to them, this internal root only lies beside the pneumogastric for a 

 very short distance, ultimately leaving it and forming the superior laryngeal 

 and pharyngeal nerves, which seem to arise from the vagus rather than 

 the accessory of Willis. 



Distribution. Beyond the ganglion of the pneumogastric, the spinal 

 accessory remains beside the trunk of the pneumogastric for scarcely an 

 inch ; it then separates from it at an acute angle whose sinus is occupied 

 by the great hypoglossal nerve, is directed backwards, passing beneath tho 

 superior extremity of the maxillary gland and levator humeri, gains the 

 supero -posterior border of that muscle, and follows it to the front of the 

 shoulder. Here it slightly ascends, crosses that region below the inner 

 face of the cervical trapezius, and is distributed to the dorsal trapezius. 



On its passage it emits : 1. One or two thick filaments to the superior 

 cervical ganglion, proceeding from the spinal by a small plexiform network 

 where the nerve separates from the pneumogastric ; 2, Near the maxillary 

 gland, a thick branch to the sterno-maxiljaris muscle ; 3, Slightly beyond 

 this, another branch destined to the anterior portion of the levator humeri : 

 4, A series of ramuscules to the cervical trapezius. 



In its course, the spinal accessory traverses the anterior part of the 

 superficial cervical plexus, and receives additional ramuscules from the 

 first, second, third, fourth, fifth, and sometimes even from the sixth cer- 

 vical nerves. 



Reduced to its medullary root, as has been described, the spinal 

 accessory animates the muscles to which it is distributed, and through them 

 has a share in expiration. By the contraction of these muscles, the ribs 

 may be maintained raised for a certain period, and cause the air to be slowly 

 expelled ; also allowing the sounds or voice produced by its passage through 

 the larynx to be modulated. Crowing is no longer possible in birds when 

 the medullary root of the spinal accessory has been divided, as has been 

 demonstrated by Bernard. 



