628 FUNCTIONS OF THE CEKEBRO -SPIN AL NERVOUS SYSTEM. 



Fm. 231. 



cord into connection, thus aiding in the co-ordination of complex move- 

 ments. For, in the first place, if the posterior columns are divided at several 



successive places, it will be found that the 

 movements of locomotion become more and 

 more disordered in proportion to the number of 

 the sections (Fig. 231), whilst it is well known 

 that locomotor ataxy, in which affection the 

 power of locomotion and of co-ordinating move- 

 ments is remarkably impaired, is associated with 

 disease of these columns. Schiff, 1 however, concludes from his experiments 

 that the posterior columns are essentially destined to conduct tactile sensa- 

 tions as opposed to those of pain or pressure ; 2 since every lesion of these 

 columns causes a permanent loss of tactile sensation, at least when the lesion 

 is in the lower part of the, cervical and the dorsal part of the cord. 



Antero-lateral Columns. These columns are chiefly composed of longitudi- 

 nally running fibres (m, Fig. 238) which conduct volitional impulses to the 

 groups of motor cells (L, Fig. 238) in the anterior coruua of the gray sub- 

 stance; but in part also of fibres proceeding from these cells and running 



transversely to emerge as the anterior 

 roots of the spinal nerves. Some an- 

 atomists, as Schroder, admit the ex- 

 istence of longitudinal cominissural 

 fibres (indicated by dotted lines in 

 Fig. 238) serving like those of the 

 posterior columns to bring different 

 segments of the cord into connection. The volitional motor fibres, though 

 responding readily to their natural stimulus, answer but slowly to direct irri- 

 tation. Feeble indications of sensibility can be obtained on irritating them, 

 which has been attributed by Claude Bernard to the presence of recurrent fibres 

 from the posterior roots. If a section of the cord be made, as in Fig. 229, 

 dividing the posterior columns alone, the animal is still capable of moving 

 all the muscles of its posterior limbs voluntarily. But if the anterior and 





FIG. 232. 



1 Centralblatt, 1872, p. 774. See also Lond. Med. Record, Jan 15th, 1873. 



2 Schiff agrees with Sanders Ezn, who has found that the tactile fibres of the pos- 

 terior roots in the lumbar region run obliquely upwards fur two or three inches before 

 they enter the posterior columns. The posterior columns of the lumbar region in 

 animals (dogs) contain the tactile nerves of the organs of generation, pelvis, anus, 

 and tail. The tactile nerves of the feet lie in other regions of the cord. Hence 

 lesions of the posterior columns in the upper part of the lumbar segment cause 

 paralysis of tactile sensation in the region of the anus, while the sensation and rn.-tion 

 of the posterior extremities remain normal In the region situated above the last 

 three cervical vertebrae there is a strand of white substance in the lateral column 

 which serves as the path by which the sensory impressions exciting the thoracic 

 movements in respiration are conducted. Lesions of these strands cau.-e absolute and 

 permanent, paralvsi* of the respiratory movements, never compensated by any of the 

 other parts of the. cord. Section of the lateral column in the upper cervical region 

 causes, along with a greater or less insensibility to tactile impressions, complete 

 immobility of the ribs during respiration. Scbitf 's investigations into the functions of 

 the lateral columns in the dorsal region have satisfied him that they do not contain 

 the conductors of the sensory imprest-ions of pain or of pressure for the hinder ex- 

 tremities. These are conveyed through the central and lateral gray substance of the 

 cord. The lateral gray substance of the right side in man, the dog, and rabbit 

 specially, and perhaps also exclusively, conducts the sensations of pain of the opposite 

 posterior limb, and viceversd. Cats, however, form an exception to this rule, for in 

 the cord <>f these animals the sensory paths do not decussate. Schiff believes that in 

 lesions of almost any part of the cord a compensatory assumption of the functions 

 of the injured parts by tho e left intact may take place. The only exception being 

 in the case of the posterior columns. 



