SPINAL NERVES 



355 



At the points wher^ the anterior and lateral terminal rami arise, connecting 

 loops may extend from one spinal nerve to another. Thus in the cervical region 

 superficial and deep nerve plexuses are formed. The deep cervical plexus forms 

 the ansa hypoglossi and the phrenic nerve (Fig. 359). 



Gang, acusticitm Vesicula andiliva 

 Gang, semilunare n. V / / Gang, radicis n. IX 



Cerebellum \ N. VI ' 



I 'Gang, petrosmn 



G i»i^ ridnn n X 



Ganf;. Froriep 

 A hypoglossus 



^ JL I.e. 



.*.j4;~ --^ N. XI 

 -Gang, nodes. 

 A . desc. cerv. 



i\ axillaris 

 ' N phrenic-US 

 ' i\. medianus 

 X. radialis 

 " A . ulnaris 

 I 111. 



N tihih 

 N. pcioHiU:^ 



Tuhu\ dutit 



IL. 



R pastil lor 

 R li I miiwlis I iluahi 

 R I I nun tin anl ini 



7S 

 N .femoral \ 

 N. obturator 



Nn. ilioing. et hypogastr. 



Fig. 359. — Reconstruction of the nervous system of a 10 mm. embryo (Streeter). X 12. 



The Brachial and Lumbosacral Plexuses.— The nerves supplying the arm 

 and leg also unite to form plexuses. In embryos of 10 mm. (Fig. 359) the trunks 

 of the last four cervical nerves and of the first thoracic are united to form a flat- 

 tened plate, the anlage of the brachial plexus. From this plate nervous cords 

 extend into the intermuscular spaces and end in the premuscle masses. The 

 developing skeleton of the shoulder spHts the brachial plexus into dorsal and 



