356 



CHORDATE ANATOMY 



Little can be said concerning the sympathetic nervous system of 

 cyclostomes. The nerves of cyclostomes, like those of Amphioxus, are 

 not medullated, so that this means of distinguishing sympathetic from 

 other fibers cannot be used. A number of observers claim to have found 



Cerebellum 



Olfcictury bulh 



Olfactory tract 



Vagus nerve N. X 

 Glossopharyngeal nerve N. IX / / 

 Acoustic nerve N. VIII / 

 Abducens nerve N. VI 



! I 



I optic nerve N. II 



Inferior lobe 



I i Oculomotor nerve N. Ill 

 ' Saccus vasculosus 

 Trochlearnerye N. IV 



Trigeminal and facial nerves Nn. V, VII 

 Fig. 313. — The brain of the dogfish, Squalus acanthias, lateral view. (From Ranson's 

 "The Anatomy of the Nervous System," courtesy of W. B. Saunders Company.) 



clusters of sympathetic ganglion cells associated with the vagus. Also a 

 plexus comparable to Auerbach's plexus of higher vertebrates is found 

 in the intestinal wall. Chromaffin cells, which have an origin in common 

 with sympathetic cells, are found in the trunk region and have a segmental 

 distribution as in mammals. 



Optic lobe 

 Epiphysis' Mesocwle 



Paraphysis 

 Cerebral hemisphere \ j 

 Olfactory tract \ " ' ' 



Olfactory bulb 



Cerebellum 

 i Metacxle 



Tubercuhtm acusticum 

 chorioidea 

 Fourth ventricle 

 ccral lobe 



Telencephalon / i ! i j '. Mctencephalon Mydenccphalon 



Preoptic recess • 'it >.i f 



rj , ,1 Mesencephalon 



Velum transver sum , [ Saccus vasculosus 

 Optic chiasma Xhird ventricle 

 Fig. 314. — The brain of the dogfish, Squalus acanthias, medial sagittal section. 

 (From Ranson's "The Anatomy of the Nervous System," courtesy of W. B. Saunders 

 Company.) 



Elasmobranchs. The nervous system of elasmobranchs shows some 

 advances above that of cyclostomes. The roof or pallium of the telen- 

 cephalon has thickened and expanded. To the corpus striatum is added 

 an epistriatum, both connected with olfactory fibers. The telencephalon 



