CEPHALIC NERVES IN GENERAL. 325 



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 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 ; whilst others are transmitted to the opposite 

 side, like those of the higher cerebral 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.* 



420. The general character and arrangement of the Cephalic nerves, as 

 distinguished from the ordinary Spinal, constitute a study of much interest, 

 when considered in relation to Comparative Anatomy, and to Embryology. It 

 appears, from what has been already stated, that the Par Vagum, Spinal 

 Accessory, Glosso-pharyngeal, and Hypoglossal nerves, may be considered 

 nearly in the light of ordinary Spinal nerves. They all take their origin ex- 

 clusively in the Medulla Oblongata ; and the want of correspondence in posi- 

 tion, 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, as long since pointed out by Rosenthal, and lately stated prominently 

 by Dr. Reid, not only decussate laterally, but, as it were, antero-posteriorly 

 ( 353). The Hypoglossal, as just stated, not unfrequently possesses a sen- 

 sory in addition to its motor root. The Glosso-pharyngeal, which is princi- 

 pally an afferent nerve, is stated by Arnold and others to have a small motor 

 root; at any rate, the motor fibres which answer to it are to be found in the 

 Par Vagum. That the Par Vagum and a portion of the Spinal Accessory 

 together make up a spinal nerve, has been already stated as probable. 



421. 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 essen- 

 tial part of the nervous system in Vertebrata ; and that the Cerebral Hemi- 

 spheres are superadded, as it were, to this. At an early period of develop- 

 ment, the Encephalon consists chiefly of three vesicles, which correspond 

 with the ganglionic enlargements of the nervous cord of the Articulata, and 

 mark three divisions of the cerebro-spinal 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 three vertebrae, in a much expanded and altered 

 condition. However improbable such an idea might seem, when the cranium 

 of the higher Vertebrata alone is examined, it at once reconciles itself to our 

 reason, when we direct our attention to that of Reptiles and Fishes ; in 

 which classes the size of the Cerebral or hemispheric ganglia is very small, 

 in comparison with that of the Ganglia of special sensation; and in which the 

 latter evidently form but a continuation of the Spinal Cord, modified in its 

 function ; so that, when we trace upwards the cavity of the spinal column 

 into that of the cranium, we encounter no material change, either in its size or 



* It may be questioned, however, whether the Hypoglossal is really paralyzed on the op- 

 posite 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 towards the palsied side ; showing that the muscles of either half are 

 sufficient to give any required direction to the whole. 

 28 



