PHYSIOLOGY, AND PATHOLOGY OF THE CHIMPANZEE. 413 



The Sympathetic Nervous System (text-figs. 45 & 46), 



The long, oval superior cervical ganglion (S.O.G) extends from 

 the level of the hard palate to the hyoid bone. It is connected 

 by communicating bi-anches to the ninth (IX) and twelfth 

 cranial nerves, and to the ganglion nodosum (G.N) and its 

 superior laryngeal (b) branch. On the left side it sends no 

 twigs direct to the cervical plexus, but it is connected to the 

 first and second cervical nerves on the right (text-fig. 45 A.) It 

 gives off pharyngeal nerves and the external carotid plexus, but 

 no cardiac nerve arises from it. The internal carotid branch 

 (I.O.N) breaks up into a plexus before it enters the skull. 



The left sympathetic runs separate from the vagus and ends 

 in the middle cervical ganglion (M.O.G) whence the following 

 branches radiate: — (1) A stout cord which divides into branches 

 accompanying the thyroidea ima artery to the thyroid gland 

 (T.B.S), tracheal nerves and cardiac nerves (O.B.S) to the deep 

 part of the cardiac plexus and plexus round branches of the 

 aortic arch. (2) Nerves to the cardiac and aortic plexus (O.B.S) 

 (.3) Oontinuation of the cord to the inferior cervical ganglion 

 (I.O.G). This also communicates with the vertebral plexus 

 (V.A.P), brachial plexus (c.B.P), and cardiac plexus. 



The right sympathetic fuses with the right vagus, but 

 separates from it lower down again, and a rich plexus of nerves 

 comes from it, both above and below, and accompanies the 

 common carotid artery to the plexus on the branches of the 

 aortic arch. The middle ganglion does not send oft" many 

 radiations as on the left side. 



The inferior cervical ganglion (I.O.G) and first thoracic 

 ganglia are fused. It gives off rami communicantes to the 

 brachial plexus (c.B.P), a thick plexus which accompanies the 

 vertebral artery (V.A.P), a nerve to the cardiac plexus, and 

 the thoracic sympathetic cord (T.O.S). 



The Thoracic Cords have fewer ganglia than the number of 

 intercostal nerves. The lefb one gives oft" the great splanchnic 

 nerve (G.S.N) at the level of the fifth and sixth thoracic nerves. 

 At the level of the diaphragm it divides into the small 

 splanchnic nerve (S.S.N) and abdominal sympathetic cord 

 (S.O). In addition to these it gives off rami communicantes to 

 the intercostal nerves and some of these are long. Aortic nerves 

 accompany the intercostal arteries to the plexus around the 

 aorta, and some of these reach the root of the lung, but were 

 very delicate at that region. 



Abdominal Gords (text-fig. 46) :— The left cord runs down and 

 passes under the left renal artery. It possesses four ganglia. 

 The first (G.l) lies at the level of the superior mesenteric artery. 

 The cord which emerges from it gives oft" nerves to the inferior 

 mesenteric plexus (I.M.P) and divides into two. The halves are 

 collected again into the second ganglion (G.2) ; this gives off" 

 rami communicantes (R.O) to the first two lumbar nerves, a 



