38 THE INVOLUNTARY NERVOUS SYSTEM 



observations have already been summarized in the previous 

 chapter, the important points being the proof of the segmental 

 nature of the terminal motor neurons of this group of involuntary 

 muscles, which lie in the ganglia of the main sympathetic chain, 

 and the non-segmental nature of the connector fibres connecting 

 these neurons with the central nervous system. As the connector 

 fibres to the whole of the ganglia of the main sympathetic chain 

 leave the cord in the thoracico-lumbar outflow, it matters not 

 whether the erection of hairs takes place on the head, body, or 

 tail ; in all cases the motor neurons of the pilomotor muscles 

 connect with the central nervous system only in the thoracico- 

 lumbar region. 



The extent of the skin area, which is supplied by the connector 

 fibres in any anterior root of the spinal nerves, is given in Langley's 

 table, which I here reproduce. 



CONNEXION OF THE SPINAL NERVES OF THE CAT FROM THE FOURTH THORACIC 

 TO THE THIRD LUMBAR WITH THOSE LATERAL GANGLIA 'OF THE SYMPA- 

 THETIC INCLUDED BETWEEN THE GANGLION STELLATUM AND THE COCCY- 



GEAL GANGLIA. 



Spinal Nerve. 



Sympathetic Ganglia. 



In close connexion with these muscles, which move hairs, are 

 the unstriped muscles which move the skin, the contraction of 

 which in hairless animals like man causes the appearance known 

 as goose skin, also the unstriped muscles underlying the skin 

 round the orifices of the body, such as the anus and vagina, such 

 a muscle as the retractor penis, and the unstriped muscles in 

 connexion with the movements of the globe of the eye and of the 

 nictitating membrane. 



In all cases the connector nerves to the motor neurons of 

 this skin musculature come out in this thoracico-lumbar outflow, 



