THE NERVOUS SYSTEM OF THE DOG 733 



divides near the middle of tlie metatarsus into two branches. Of these, the internal 

 branch constitutes the first plantar common digital nerve (N. dig. comm. plant. I). 

 Tlie outer branch desccnids on the superficial flexor tendon and divides into three 

 plantar metatarsal nerves (Nn. met. plant. II, III, IV), which unite with the 

 plantar conunon tligital nerves. The external plantar nerve passes down between 

 tlie flexor tendons, sends twigs to the muscles on the plantar surface of the metatar- 

 sus, and divides into three plantar common digital nerves (Nn. dig. comm. plant. II, 

 III, IV). These descend with the deep plantar metatarsal arteries in the second, 

 third, and fourth intermetatarsal spaces, receive the plantar metatarsal nerves, 

 and divide into plantar proper digital nerves, which pass down the opposed surfaces 

 of the second to the fifth digits. 



The sympathetic system presents few special features worthy of mention. 

 The superior cervical ganglion lies above the ganglion nodosum close to the cranial 

 base and internal to tli(> oiMgin of the internal carotid and occipital arteries. It 

 forms connections directly or through the carotid plexus with the last seven cranial 

 and first cervical nerves. The cervical trunk unites with the vagus so intimately 

 as to form a vago-sympathetic trunk. There may be a small middle cervical 

 ganglion in front of the inferior cervical ganglion. The latter is usually distinct 

 from the first thoracic ganglion, which is stellate and lies on the longus colli opposite 

 the second rib and intercostal space. 



