HYPOGLOSSAL NERVE. CEPHALIC NERVES IN GENERAL. 693 



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 paraly- 

 sis, 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 paralyzed 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 consequently directed only by the 

 muscles of the other side, which will not act in a straight direction, when unan- 

 tagonized 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, whilst others are trknsmitted to the oppo- 

 site side, like those of the higher cephalic nerves ; and the cause of paralysis 

 may affect one or other of these sets of roots more particularly. Whatever 

 may be the validity of this explanation, the circumstance is an interesting one, 

 and well worthy of attention. 1 



721. The general character and arrangement of the Cephalic nerves, as dis- 

 tinguished from the ordinary Spinal, constitute a study of much interest, when 

 considered in relation to Comparative Anatomy, and to Embryology. It ap- 

 pears, from what has been already stated, that the Pneumogastric, Spinal Ac- 

 cessory, Grlosso-pharyngeal, 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 ( 711). The Hypoglos- 

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

 root. The Grlosso-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 Accessory 

 together represent a spinal nerve, may be regarded as probable from what has 

 been already said of their relations. 



722. Leaving these nerves out of the question, therefore, we proceed to the, 

 rest. Comparative anatomy, and the study of Embryonic development, alike 

 show that the Spinal Cord and Medulla Oblongata constitute the most essential 

 part of the nervous system in Vertebrata ; and that the Cerebral Hemispheres are 

 superadded, as it were, to this. At an early period of development, the Ence- 

 phalon consists chiefly of four vesicles, which correspond with the ganglionic 

 enlargements of the nervous cord of the Articulata, and mark four divisions of 

 the Cerebro-Spinjd axis ; and, in accordance with this view, the Osteologist is 

 able to trace, in the bones of the cranium, the same elements which would form 

 four vertebrae, in a much expanded and altered condition. 3 However improba- 



1 It may be questioned, however, whether the Hypoglossal is really paralyzed 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 some- 

 times directed from and sometimes towards the palsied side; showing that the muscles of 

 either half are sufficient to give any required direction to the whole. 



2 See "Princ. of Phys., Gen. and Comp.," Am. Ed., g 320, t ; and Prof. Owen's "Arche- 

 type Skeleton." 



