136 THE BKAIN OF REPTILES 



and probably is, a considerable amount of independent 

 activity on the part of the ' Sympathetic System,' the action 

 of its several parts is also subject to the controlling and 

 regulating influence of certain cerebro- spinal centres, with 

 which they are connected in the manner above referred to. 



In the Suctorial Fishes and the Lepidosiren, the ' Sym- 

 pathetic System ' is said not to exist, though the Cerebral 

 Systemic Nerves are large and widely distributed over the 

 viscera. In the Sharks and Rays, also, this system is ill- 

 developed, but in the majority of osseous Fishes it consists 

 of a cord on each side of the spine, forming connections 

 wilh the cerebral and spinal nerves, and in some of these 

 situations developing small ganglia and sending off 

 branches towards the viscera, which unite with others 

 from the Yagus nerve, so as to form large median 'plex- 

 uses,' or ' plexuses ' and ganglia, whence multitudes of 

 fibres are distributed to the different internal organs. 

 Many differences of detail occur in different Fishes. 



In Reptiles, also, there are various minor modifications ; 

 but, on the whole, the connections of the ' Sympathetic 

 System ' with spinal nerves are more developed in these 

 animals, and the Ganglia at such points of junction are 

 more numerous and distinct. In Birds the distribution 

 of the Visceral System of Nerves also, in the main, tends 

 to approximate pretty closely to the general plan above 

 indicated, which will be described in further detail when 

 we come to speak of its more complex development among 

 higher Vertebrates. 



By means, therefore, of this double set of Visceral 

 Nerves, the internal organs are brought into close relation 

 with one another, as well as with the Spinal Cord and 

 wit-li the Brain. 



We are not fairly entitled to measure the intensity 

 of the systemic impressions of a Fish, a Reptile, or a 



