EXAMINATION OF SOME SPINAL NERVES 
165 
Reflexes Elicited by Blows. 
A tap on the ischial callosity (tuber ischii) in the Monkey elicits excellently a bilateral 
adduction of the thighs. 
A tap upon the spinal column (skin removed) at the level of the iliac crests evokes rotation 
outwards of both thighs, with slight extension of both knees. This must be similar to a reflex 
mentioned by Sternberg* as of clinical importance ; it involves action of the glutai. 
A tap upon the articular surface of the lower end of femur evokes contraction in the 
adductors of both thighs; the contraction is bilaterally symmetrical, or more often greater on the 
contra-lateral side. 
A tap on lower end of femur, or on insertion of tendo patellae usually excites dorso-flexion 
of ankle, with slight inversion of foot. This seems to be 'Erb's tibialis anticus reflex' of 
clinicians ; in my experiments extensor longus digitorum replies more amply than does tibialis anticus. 
The tap generally elicits dorso-flexion of the contra-lateral as well as of the idio-lateral ankle. 
I am not inclined to consider any of the above to be true cross-reflexes. The so-called 
cross knee-jerk and perhaps the cross-adductor reflex are not cross-reflexes. That they are reflexes 
seems certain from the length of their latent period estimated by the time-measurements of 
BuRCKHARDT,t recently repeated with a similar result by Gotch.:]: The former is contra-lateral 
and reflex, but not a cross-reflex, for I find it persist after complete longitudinal splitting of the cord 
from a lumbar transection above to the coccygeal nerves below. It must be excited by jar as 
suggested by Waller and Prevost.§ And other 'jar' reflexes are flexion of hip, protrusion of 
anus, protrusion of vaginal orifice, all readily excited by a tap on an unyielding part. All the 
'jar' reflexes implicate parts easily moved by reflex action, and are cut out by section of the appro- 
priate sensory roots on their own side, /.f., the contra-lateral to application of blow, and not by 
section of the sensory roots on the side of the blow given. At first sight, inasmuch as they are 
bilaterally symmetrical, they appear as cross-reflexes, which supports PFLticER's 'Law of Reflex 
Symmetry.' I would apply Waller and Prevost's explanation of excitation by transmission of 
mechanical vibration to them as to the so-called cross knee-jerk. I would differ from Waller 
and Prevost, however, in so far that, if I understood their meaning aright, they consider the 
vibration acts as a direct stimulus to the muscle or its motor nerve. I think, on the other hand, 
the jar excites the afferent nerve-fibres of the nerve-roots corresponding with the muscles, and 
excites them at, or just peripheral to, the ganglion. It is remarkable how distinctly even a slight 
tap upon the end of one femur is felt by holding the lower end of the other femur, particularly 
in some positions of the thigh, especially, I think, when the thighs are somewhat abducted. 
Some Features of the Muscular Contractions Occurring in Spinal Reflexes. 
When spinal depression is great and the reflex movements diflicult to evoke, they are 
usually characterized by the following features : — feebleness, restriction of scope, minute tremor, 
and brevity of duration. As they improve they become more ample, more vigorous, less 
* 'Die Sehnenreflexe,' Vienna, 1893. 
-J- 'Ueber Sehnenreflexe,' Bern, 1877. 
I ' Journ. of Physiol.,' vol. 20. 
Revue Meilicale de la Suisse Roman<le,' iSiii, 
