Lin H, Hou C-L, Zhong G, Xie Q, Wang S. Reconstruction of reflex pathways to the atonic bladder after conus medullaris injury: preliminary clinical results.
Microsurgery. 2008;28(6):429-35

Some text from this paper:
In Method: Twelve months after operation, the patients were directed to scratch or gently squeeze the T1 dermatome when the bladder was full to try to initiate voiding.

Results part: Seven of the 10 patients (70%) experienced recovery of bladder storage and voiding functions. These patients voided by stimulating the skin-CNS-bladder reflex (scratching or gently squeezing the T11 dermatome), which became functional around 18 months postoeratively. About 5-10 seconds after the beginning of skin stimulation, the patients begin to void.

这个是侯文的挠皮肤反射弧示意图。因为他使用了T11的root，离S2相当远，所以他使用了一段自身供体神经做连接。

下面是dermatomes的分布图，可见T11的dermatome在下腹部。图选自我正在读的Dale Purves的Neuroscience。