THOEACIC PAET OF THE SYMPATHETIC SYSTEM. 759 



of the facial, in the foramen lacerum. By their union the pterygoid nerve is 

 formed, which, after traversing the pterygoid canal, ends in the spheno-palatine 

 ganglion. The carotico-tympanic nerves pass to the tympanic plexus. This plexus, 

 formed by the carotico-tympanic nerves, the tympanic branch of the glosso- 

 pharyngeal, and a twig from the genicular ganglion of the facial nerve, is placed 

 on the labyrinthic wall of the tympanum. It supplies the mucous lining of the 

 tympanum and auditory tube; and the lesser superficial petrosal nerve passes 

 from it to the otic ganglion. 



Plexus Cavernosus. The cavernous plexus communicates with (a) the oculo-motor, 

 (6) the trochlear nerve, and (c) the ophthalmic division of the trigeminal nerve ; 

 it also (d) supplies twigs to the hypophysis (pituitary body), and (e) forms the 

 sympathetic root of the ciliary ganglion. This may pass to the ganglion inde- 

 pendently, or it may be incorporated in the long root of the ganglion from the 

 naso-ciliary branch of the ophthalmic nerve. 



GANGLION CERVICALE MEDIUS. 



Central Communicating Branches. 1. Gray rami commuiiicantes arise from 

 the ganglion or from the connecting cord, and join the anterior rami of the fifth 

 and sixth cervical nerves. 2. The ansa subclavia (Vieussenii) is a loop of com- 

 munication from this ganglion, which, after passing in front of and supplying offsets 

 to the subclavian artery and its branches, joins the inferior cervical ganglion. 



Peripheral Branches of Distribution. 1. Heart. A slender middle cardiac 

 branch descends, either separately or in company with other cardiac nerves, behind 

 the large vessels into the thorax, where it ends in the deep part of the cardiac 

 plexus on each side. 



2. Thyreoid Gland. Branches extend medially along the inferior thyreoid 

 artery to supply the thyreoid gland. 



When the middle ganglion is absent the branches described arise from the 

 necting cord. 

 GANGLION CERVICALE INFERIUS. 

 Central Communicating Branches. 1. Gray rami communicantes arise from 

 this ganglion for the anterior rami of the seventh and eighth cervical nerves. 

 2. The ansa subclavia already mentioned connects the middle and inferior ganglia 

 over the front of the subclavian artery. 3. A communication frequently occurs 

 with the recurrent nerve. 



Peripheral Branches of Distribution. 1. Heart. An inferior cardiac branch 

 is given off on each side to enter the deep cardiac plexus. 



2. Vessels. (a) The vertebral plexus is a dense plexus of fibres surrounding 

 the vertebral artery and accompanying its branches in the neck and the cranial 

 cavity. (6) The subclavian plexus is derived from the ansa subclavia (subclavian 

 loop), and supplies small offsets to the subclavian artery. It gives branches to the 

 internal mammary artery, and communicates with the phrenic nerve. 





II. PAES THOEACALIS SYSTEMATIS SYMPATHICI. 



The thoracic part of the sympathetic trunk lies behind the pleura, in front 

 of the necks of the ribs, and the intercostal vessels and nerves. It consists of a 

 number of ganglia of an irregularly angular or fusiform shape, joined together by 

 connecting bands of considerable thickness. The number of ganglia is usually 

 ten or eleven; but the first and sometimes others may be so fused with the 

 neighbouring ganglia as to reduce the number still further. 



This part of the sympathetic trunk is characterised by its union with the thoracic 

 spinal nerves. Each thoracic nerve, with the probable exception of the first, sends 

 a visceral branch (white ramus communicans) to join the gangliated trunk in the 

 thorax. These white rami separate into two main streams in relation to the 

 sympathetic trunk. Those of the upper five nerves are for the most part directed 

 upwards to be distributed through the cervical part of the sympathetic trunk 



49 c 



