176 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



tetrapoda these are grouped into a single chief trunk on either side 

 in the lower groups, while in the mammals there is an additional one 

 on the ventral side. 



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MM, 



Fig. 185. — A, diagram of collector nerve; B, of a nerve plexus, after Braus: C, branchial 

 plexus of Salamandra maculata, after Fiirbringer. 



Fig. 186. — Nerves no. 25-37 of a Mustelus embryo 24 cm. long, with collector nerve 

 after Punnett. Dotted line shows limit of coelom; g, pelvic girdle. 



In the fishes the lumbo-sacral plexus and its nerves is reinforced by 

 a collector nerve which extends from and connects some of the 

 more anterior segmental nerves with the appendage, though without 

 such an exchange of fibres as are found in a plexus. Besides, in the 



