662 FUNCTIONS OF THE CEREBRO-SPINAL NERVOUS SYSTEM. 



into the Cerebellum, are not, as has been supposed, the conductors of sensory 

 impressions. 2. That whilst hypenesthesia occurs on the same side of the 

 body when the Spinal Cord is injured, especially in its posterior part, it ap- 

 pears on the opposite side of the body when a section is made either of the 

 anterior or posterior surface of the Pons ; and this he believes to favor his 

 view of the decussation of the sensory fibres in the Cord, and to be opposed 

 to the old view of the decussation of these fibres below the Tubercula Quad- 

 rigemina, or in the substance of the Pons itself. 3. The transmission of 

 sensory impressions in the Pons appears to be chiefly effected by its central 

 portion, whilst the anterior portion is chiefly instrumental in the conduction 

 of the mandates of the Will to the Muscles. The experiments of Longet 

 led him to the conclusion, that the Tuber Annulare, the structure of which 

 is very complicated, is an independent centre of sensation and of motor 

 power ; but they do not afford any clear information as to its special attri- 

 butes. He states, however, that convulsive movements are excited by irri- 

 tating it, and especially by the transmission of an electric current through 

 its substance. These movements, however, according to the testimony of 

 Dr. Todd, appear to be of a different character from those which are excited 

 by the application of the same stimulus to the Spinal Cord and Medulla 

 Oblongata ; for he states that while the convulsions excited by the transmis- 

 sion of the current of the magneto-electric machine through the parts just 

 named, are tetanic, the muscles being thrown into a state of fixed contrac- 

 tion, those which ensue when the current is transmitted through the region 

 of the Mesocephale and Corpora Quadrigemiua, are epileptic, being com- 

 bined movements of alternate contraction and relaxation, flexion and exten- 

 sion, affecting the muscles of all the limbs, of the trunk, and of the eyes, 

 which roll about just as in epilepsy. 1 



531. The evidence afforded by Pathology regarding the functions of these 

 Ganglionic masses is not altogether self-consistent; but this arises, probably, 

 from the circumstance that the effects of morbid changes (particularly of 

 sanguineous effusions) in any part of the Encephalon, extend themselves to 

 other parts than those in which the obvious lesions are found ; as is abundantly 

 proved by the great variety of phenomena which present themselves as the 

 results of lesions apparently similar, and by the similarity of the phenomena 

 that are frequently consequent upon lesions of very different parts. It is. es- 

 tablished by abundant evidence that disease of the Corpora Striata, or Thalami 

 Optici, or haemorrhage into these bodies produces bemiplegia, or paralysis of 

 the opposite side. This paralysis, however, is not uniform, but affects chiefly 

 the arm and leg, and in a less degree the face, whilst sensation is usually only 

 slightly affected, or escapes altogether. An ingenious attempt has been made 

 by Dr. Broadbent 2 to explain the phenomena observed in these cases. He 

 observes that the relative situation of the two ganglia (Corpus Striatum and 

 Optic Thalamus) will in some measure account tor the circumstance that 

 sensation so frequently escapes when motor power is lost; since the Corpus 

 Striatum the motor ganglion is in front of and external to the Thalamus, 

 and may therefore easily be extensively damaged without involving the latter, 

 or the fibres passing from it to the Cord. The Thalamus the sensory ganglion 

 on the other hand, lying behind the Corpus Striatum, and upon the fibres 

 connecting it with the Cord, can scarcely be seriously affected without injury 

 to these fibres or the Corpus Striatum itself. Again, the Optic Thalamus, 

 according to hypothesis, standing with respect to the Corpus Striatum in the 



1 Lumleian Lectures, On the Pathology and Treatment of Convulsive Diseases, in 

 Medical (Jazette, May llth, 1849. 

 J Med.-Chir. Rev., April, 1866. 



