644 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



supply the genital organs. The act of Parturition, however, seems to be 

 less dependent upon the Spinal Cord ; for, as will be shown hereafter (chap. 

 xviii, sect. 3), the contractions of the Uterus, which are alone sufficient to 

 expel the foetus when there is no considerable resistance, are not to be 

 regarded as altogether "reflex;" and it is only in the co-operation of those 

 associated muscles which come into play in the second stage of labor, when 

 the head is passing through the os uteri and is engaged in the pelvic cavity, 

 that the assistance of the Spinal Cord and its nerves is called in. These 

 movements, like those of Defecation, may be to a certain extent promoted 

 or restrained by voluntary effort; but when the exciting influence (the pres- 

 sure of the head against the parietes of the vaginal canal) has once been 

 fully brought into operation by the uterine contractions, the Will has little 

 power over them, either in one way or the other. The antagonizing influ- 

 ence of the sphincter vaginte seems, like that of the sphincter ani, to be de- 

 pendent upon the Spinal Cord ; and thus it happens that when its tension 

 and that of other muscular parts has been destroyed by death, whilst the 

 uterus still retains its contractility, the power of the latter has sufficed for 

 the completion of the parturient process, the child being expelled after the 

 respiratory movements have ceased. [Goltzand Frensberg have shown that 

 in the lumbar portion of the cord a centre for the iunervatiou of the uterus 

 is seated. Masius and Vanlair state that feeble excitation of the superior 

 third of the lumbar portion of the cord causes an active dilatation of the anus, 

 and an elevation of the tail (dog), whilst moderate irritation of the middle 

 third caused a contraction of the sphincter, and a lowering of the tail. An 

 intense irritation of the one or the other of these parts causes these actions to 

 become rhythmical. They hold that the rhythmic centre contains mainly 

 the ano-spinal centre. 1 ] 



508. The Spinal Axis is not merely the instrument whereby the move- 

 ments essential to the maintenance of the organic functions are sustained ; 

 it is also subservient to other muscular actions, whose character is essentially 

 protective. Thus it was ascertained by Dr. M. Hall 2 that, if the functions of 

 the Brain be suspended or destroyed without injury to the Spinal Cord and 

 its nerves, the Orbicularis muscle will contract, so as to occasion the closure 

 of the eyelids, upon their tarsal margin being touched with a feather. This 

 fact is iiiteresting in several points of view. In the first place, it is a char- 

 acteristic example of an adaptive action, occurring under circumstances in 

 which volition cannot be imagined to guide it, and in which there is no valid 

 reason to believe that sensation directs it. Further, it explains the almost 

 irresistible nature of the tendency to winking, which is performed at short 

 intervals by the contraction of the Orbicularis muscle; this is evidently a 

 reflex action, capable of being in some degree restrained (like that of res- 

 piration) by the will, but only until such a time as the stimulus (resulting 

 perhaps from the collection of minute particles of dust upon the eyes, or 

 from the dry ness of their surface in consequence of evaporation), becomes 

 too strong to be any longer resisted. The nervous channel through which 

 this action is performed, is completed by the first branch of the Fifth and 

 the Portio Dura of the Seventh. Again, we have in sleep or in apoplexy 

 an example of this purely spinal action, unbalanced by the influence of the 

 will, which, in the waking state, antagonizes it by calling the levator palpe- 

 ])],! into action. As soon as the will ceases to act, the lids droop, and close 

 over the eye so as to protect it; and if those of a sleeping person be sepu- 



1 [Chicago Jour, of Nervous Diseases, vol. ii ] 



2 Memoirs on the Nervous System, 1837, p. 61. 



