32 ELEMENTARY BIOLOGY. [CHAP. 



SympatJietic, 



The sympathetic system consists of ganglia, usually ten 

 in number on each side, connected by longitudinal com- 

 missures, and situated on the ventral face of the vertebral 

 column ; in the region of the dorsal aorta they come into 

 close relation with it. Each sympathetic ganglion is joined 

 by a communicating filament or ramus witli one of the 

 spinal nerves, and the most anterior ganglia are connected, 

 in the same way, with the ganglia of the ninth and tenth 

 cerebral nerves. Thence a delicate cord passes into the 

 cranial cavity on the inner side of the periotic capsule, and 

 unites with the Gasscrian ganglion. 



The branches of the sympathetic accompany the vessels, 

 and large branches are given to the viscera. 



The sheath of the ganglion of each spinal nerve encloses 

 a milk-white body {pcrigangliojiic gland) whose function is 

 unknown. Each consists of a tubular gland, lined by a 

 single-layered epithelium and containing calcareous matter 

 in a finely crystalline state. AVhen fully formed these glands 

 force their way through the inter-vertebral foramina, appearing 

 as a series of concretionary masses lying around the spinal 

 nerves at their points of exit from the column, and alternating 

 with the bases of the transverse processes of the vertebrae. 



The Olfactoty organs occupy all the space between the 

 mesethmoid cartilage, the antorbital processes, and the 

 premaxillae and maxillae, and open in front and externally 

 by the external nares, behind and internally, into the mouth- 

 cavity, by the posterior nares. Each consists of an essential 

 part or olfactory sac, the inner face of which is lined by a 

 peculiar epithelium, which receives the olfactory branches 

 of the trigeminal nerves, and an accessory part consisting of 

 a partly cartilaginous, partly bony, capsu/e. 



