240 ELEMENTS OF MAMMALIAN ANATOMY 



The lesser sciatic nerve comes chiefly from the second and 

 third sacral nerves. It suppHes the region of the anus and the 

 biceps muscle. 



Other nerves given off from the sacral plexus are the glutei 

 and pudic nerves supplying the buttock muscles and external 

 genital organs. 



THE SYMPATHETIC NERVOUS SYSTEM 



The sympathetic nervous system is composed chiefly of a pair 

 of nerve-cords extending from the base of the skull to the root of 

 the tail, a number of ganglia and branches supplying the thoracic 

 and abdominal viscera, and numerous minute libers supplying 

 the muscular walls of the blood-vessels in all parts of the body. 

 The sympathetic system supplies all non-striped or involuntary 

 muscles in any part of the body. The two branches connecting 

 each spinal nerve with a sympathetic nerve-cord are called rami 

 c mm unic antes. 



In order to demonstrate this system successfully, one should 

 use a lean injected specimen. After the cat has been securely 

 nailed on its back to the tray, the entire ventral half of the 

 thoracic and abdominal walls should be removed. By pushing 

 the heart and lungs to the left side a white cord about one milli- 

 meter in diameter may be seen lying near the median dorsal line 

 (Fig. 116). The left cord may be found in a similar manner and 

 both followed craniad and caudad, noting their numerous 

 branches in accordance with the following description. 



The sympathetic nerve -cord begins in the superior cervical 

 ganglion lying near the angle of the mandible, beneath the sub- 

 maxillary and lymphatic glands. This ganglion is about the 

 shape of a grain of wheat, but not more than half so large, and 

 is adjacent to the small vagus' ganglion on the dorsal side of the 

 carotid artery. The ganglia are masses of large nerve cells and 

 occur at regular intervals on the sympathetic cords in the body 

 cavity, and are present also on some of the branches of the cords 

 (Fig. 117). On the cords there are three pairs of cervical ganglia, 



