THORACIC PART OF CORD. 367 



(V) Motor fibres to the involuntary muscle of the orbit and eyelids, from the highest 

 four or five dorsal nerves (Lang-ley). 



(V) Vaso-motor fibres of the head. Vato-GOnstriotor fibres are given off in the dog 1 and 

 cat chiefly by the second, third, and fourth dorsal nerves, in the rabbit by the dorsal 

 nerves from the second to the eighth (Langley). There is also some evidence as to the 

 existence of mso-dilator filnr*. but the origin of these has not been fully ascertained. 



(d] Secretory fibres of the submaxillary gland, mainly from the second and third dorsal 

 nerves. 



(^) Pilo-motor fibres of the face and neck, in the monkey arising from the second, 

 third, fourth, and fifth dorsal nerves (Sherrington). 



In all the foregoing groups the fibres of spinal origin terminate, and fibres of sympathetic 

 origin arise, in the superior cervical ganglion. 



(/) Accelerator fibres of heart, derived from the upper four or five dorsal nerves, but 

 chiefly from the second and third. The spinal fibres end and sympathetic fibres begin in the 

 middle and lower cervical (perhaps also the first thoracic) ganglia. 



THORACIC PART OF THE GANGLIATED CORD. 



In the thorax the gangliated cord is placed at the side of the spinal column, along 

 a line passing over the costo-central articulations. It is covered by the pleura, and 

 crosses the intercostal blood-vessels. 



The ganglia are commonly eleven in number, seldom twelve. The first, when 

 distinct, is larger than the rest, and lies at the vertebral extremity of the first 

 intercostal space ; but it is often blended with the lower cervical ganglion. The 

 succeeding ganglia are small, oval or triangular in form, and correspond generally 

 to the heads of the ribs from the third to the eleventh ; while the last is placed 

 a little in front of the head of the twelfth rib, about the upper border of the last 

 dorsal vertebra. 



Connection with spinal nerves. The branches of connection between the 

 dorsal nerves and the ganglia of the sympathetic are usually two in number for each 

 ganglion, one of these being white and the other grey (p. 358). 



BRANCHES OF THE GANGLIA. 



The branches furnished by the upper four or five ganglia are small, and are dis- 

 tributed in great measure to the vertebrae and ligaments, and to the descending 

 thoracic aorta (fig. 232), on which they form, together with filaments proceeding 

 lower down from the great splanchnic nerve, a slender network (plexus aorticus 

 thoracalis). From the second, third, and fourth ganglia offsets pass also to the 

 posterior pulmonary plexus (p. 268). 



The branches furnished by the loiver six or seven ganglia unite into three cords 

 on each side, which pass down to join plexuses in the abdomen, and are dis- 

 tinguished as the great, the small, and the smallest splanchnic nerves (abdominal 

 splanchnics of Gaskell). 



The great splanchnic nerve is formed by the union of roots which are given 

 off by the thoracic ganglia from the fifth or sixth to the ninth or tenth inclusive. 

 The trunk thus constituted descends obliquely forwards over the bodies of the dorsal 

 vertebras, and after perforating the crus of the diaphragm terminates in the upper 

 part of the semilunar ganglion : some of the fibres may occasionally be followed to 

 the suprarenal body and the renal plexua This nerve is remarkable from its white 

 colour and firmness, due to its consisting in large part (four-fifths according to 

 Riidinger) of medullated fibres, which are continued directly from the spinal nerves ; 

 from the highest root they may be traced upwards along the sympathetic cord as far 

 as the third thoracic ganglion and nerve, or even higher. 



In the chest the great splanchnic nerve is not unfrequently divided into parts, 

 and forms a plexus with the small splanchnic nerve. In many cases also a small 



i. A 2 



