242 VERTEBRATE ZOOLOGY 



and the internal jugular vein. A short distance in front of the 

 first rib they separate from each other, and the sympathetic, which 

 is the smaller and more dorsal of the two, passes into the thorax. 



Three large ganglia lie in the course of the cervical portion of 

 the sympathetic cord on each side, the superior and inferior cer- 

 vical and first thoracic ganglia. The first of these marks the 

 anterior end of the sympathetic system; it is a large ganglion 

 just back of the base of the skull, on the side of the neck and 

 close to the ganglion nodulosum of the vagus. The other two are 

 at the base of the neck near the first rib and are joined together 

 by two nerves. 



Two large nerve plexuses, the cardiac and the solar, and several 

 smaller ones, belong to the sympathetic system. The cardiac 

 plexus lies at the anterior end of the heart, around the base of the 

 aorta and the pulmonary artery. The solar plexus lies between 

 the fundus of the stomach, the dorsal portion of the diaphragm, the 

 suprarenal bodies, and the aorta. It consists of two ganglia— the 

 large cceliac, or semilunar, ganglion, which lies near the superior 

 mesenteric artery, and the smaller mesenteric ganglion— and of 

 nerves which radiate from these ganglia in all directions. These 

 ganglia are joined with the longitudinal sympathetic nerve by 

 several nerves, of which the great splanchnic is the largest. This 

 nerve separates from the sympathetic in the thorax, pierces the 

 diaphragm, and goes directly to the cceliac ganglion. 



Exercise 33. Draw a diagram of the sympathetic system so far as 

 observed. 



The Special Sense Organs; the Eye. The eyeball, together with 

 its muscles, glands, and other accessory organs, lies within the 

 bony orbit. Toward the outside the eye is protected by the upper 

 and lower eyelids and the nictitating membrane. The eyelids are 

 folds of the skin; they have no eyelashes, but are covered with 

 hair, like the rest of the body. 



The nictitating membrane is situated at the inner corner of the 

 eye, over which it moves. Pull it with forceps. It is stiffened by 

 a cartilage, whose position is shown by the ridge it produces. A 

 thin, transparent membrane called the conjunctiva covers the inner 



