NERVOUS SYSTEM OF AVES. 125 



converge ventrad of the oesophagus and unite above the pre- 

 ventriculus, supplying that part, the gizzard, and ultimately com- 

 municating with the splanchnic plexus of the sympathetic. In 

 the Eagle the pneumogastric is recruited by an ^ accessorius ' nerve 

 arisino' behind the third cervical. 



The hypoglossal nerve (9th pair) escapes by one or two pre- 

 condyloid foramina. It is very slender at its origin ; passes to the 

 front of the nervus vagus, partly uniting with, as it crosses over, 

 this nerve, and in that situation it detaches a filament to the hyo- 

 laryngeal and long tracheal muscles. The trunk of the hyo- 

 glossal next crosses the glossopharyngeal nerve, passing forward 

 to sujiply the hyoglossal and lingual muscles. 



The spinal nerves arise by motory (anterior or ventral) and 

 sensory (posterior or dorsal) roots of nearly equal size ; but the 

 anterior have more numerous filaments. The ganglion on the 

 posterior root is proportionally large. In the sacral region of 

 the spine, the anterior and posterior roots escape by distinct fora- 

 mina, and can be separately divided without laying open the 

 bony canal, but they are deeply seated and well protected by the 

 anchylosed processes of the sacrum and the extended iliac bones. 



The cervical nerves vary with the number of the vertebras from 

 ten to twenty-three : each nerve divides ; the anterior branch sup- 

 plying the muscles and the skin, the posterior branch the muscles 

 chiefly. Those of the lower cervicals form a plexus, supplying 

 the scapular muscles, and communicate with the lowest cervical 

 nerve going to the brachial plexus. Only the last two or three 

 j)airs, fig. 38, u' v!' , of cervical nerves concur in the formation of 

 this plexus, which is completed by the first pair or two of dorsal 

 nerves v. The other dorsal nerves, after giving filaments to the 

 intercostals and diaphragmatic muscles, pass to the skin at the 

 sides of the trunk. 



The sacral nerves have no other peculiarity than their mode of 

 passing out of the spinal canal : they form exclusively the plexus 

 analogous to the lumbar and sacral, fig. 38, iv. The terminal 

 sjoinal nerves supply the muscles and skin of the cloaca and tail. 



The hracliial plexus, formed by the two or three last cervical 

 and one or two first dorsal nerves, soon becomes blended into a 

 single fasciculus whence all the nerves of the wing are derived. 

 The internal cutaneous nerve passes from the axilla along the 

 inner and back part of the humerus, bends round the inner 

 (ulnar) side of the elbow joint ; it supplies the skin. The next 

 branch distributes filaments to the muscles 22, 24, fig. 35 ; sends 

 off the ^ circumflex ' nerve which supplies the latissimus dorsi, 



