CEPHALIC NERVES HYPOGLOSSAL NERVE. 625 



in Man it still manifests an irregularity, in having only a single root, yet 

 this irregularity is often shared by the first cervical nerve, which also has 

 sometimes an anterior root only. 1 The Hypoglossal nerve is distributed not 

 merely to the tongue, but to the muscles of the neck which are concerned 

 in the movements of the larynx ; and the purpose of this distribution is prob- 

 ably to associate them in those actions which are necessary for articulate 

 speech. Though all the motions of the tongue are performed through the 

 medium of this nerve, yet it would appear, from pathological phenomena, to 

 have at least two distinct connections with the nervous centres; for in many 

 cases of paralysis, the masticatory movements of the tongue are but little 

 affected, when the power of articulation is much injured or totally destroyed ; 

 and the converse may be occasionally noticed. When this nerve is para- 

 lyzed on one side, in hemiplegia, it will be generally observed that the tongue, 

 when the patient is directed to put it out, is projected towards the palsied 

 side of the face : this is due to the want of action of the lingual muscles of 

 that side, which do not aid in pushing forward the tip ; the point is conse- 

 quently directed only by the muscles of the other side, which will not act in 

 a straight direction, when unantagonized by their fellows. It is a curious 

 fact, however, that the Hypoglossal nerve seems not to be always palsied on 

 the same side with the Facial, but sometimes on the other. This has been 

 suggested to be due to the origination of the roots of this nerve from near 

 the point at which the pyramids of 'the medulla oblongata decussate, so that 

 some of its fibres come off, like those of the spinal nerves, without crossing, 

 Avhilst others are transmitted to the opposite side, like those of the higher 

 cephalic nerves; and the cause of paralysis may affect one or other of these 

 sets more particularly. Whatever may be the validity of this explanation, 

 the circumstance is an interesting one and well worthy of attention. 2 The 

 Hypoglossal nerve, according to Vulpian, 3 contains vaso-motor fibres, the 

 irritation of which causes the vessels supplying the submaxillary gland to 

 contract. Its section is followed by the dilatation of these vessels. 



498. The general limnology of the Cephalic nerves, considered with reference 

 to the ordinary Spinal, constitutes a study of much interest. It appears, from 

 what has been already stated, that the Pueumogastric, Spinal Accessory, 

 Glosso pharyugeal, and Hypoglossal nerves, may be considered nearly in the 

 light of ordinary Spinal nerves. They all take their origin exclusively in 

 the Medulla Oblongata ; and the want of correspondence in position between 

 their roots and those of the Spinal nerves, is readily accounted for, by the 

 alteration in the direction of the columns of the Spinal cord, which not only 

 decussate laterally, but, as it were, antero-posteriorly ( 488). The Hypo- 

 glossal, as just stated, not unfrequently possesses a sensory in addition to its 

 motor root. The Glosso-pharyngeal, which is principally an afferent nerve, 

 has a small motor root ; but most of the motor fibres which answer to it are 

 to be found in the Pneumogastric. That the Pneumogastric and Spinal Ac- 

 cessory together represent a Spinal nerve, may be regarded as probable from 

 what has been already said of their relations. Leaving these nerves out of 

 the question, therefore, we proceed to the rest. Comparative anatomy, and 



1 See Vulpian's Essay on the Posterior or Ganglionio Root of the Bypoglossa! 

 JJerve in various Animals, Journal de la Physiologie, 1862, p. 5. 



2 It may be questioned, however, whether the Hypoglossal is really paralvzed on 

 the opposite side from the Facial in such cases. An instance has been communicated 

 to the Author by Dr. W. Budd, in which the hypoglossal nerve was completely 

 divided on one side; and yet the tip of the tongue, when the patient was desired to 

 put it out, was sometimes directed from and sometimes iowards the palsied side; 

 showing that the muscles of either half are sufficient to give any required direction 

 to the whole. 



3 Gaz. Hebdomndaire, 1873, No. 21. 



