-146 THE TISSUES. 



Fig. 289. teric vessels of the frog. 3. The thicker 



fibres become the finest kind, and ultimately 

 non-medullated embryonic fibres, in all pro- 

 bability. But nothing precise is yet known re- 

 specting their terminations in the heart, lungs, 

 stomach, intestine, kidneys, spleen, liver, ute- 

 rus, &c. 



The many plexuses of the great sympa- 

 thetic, and which affect a relationship to the 

 Apoiar nerve-ceils from the aorta an( j itg abdominal subdivisions, present 



cardiac ganglia of the frog ; 



one within the origin of a no hlStologlCal peculiarities. 



nerve-tube. Magnified 350 



diameters. (Kolliker.) 



3. The Encephalic Nerves. 



The twelve pairs of nerves rising from the encephalon correspond 

 (except the first, second, and eighth pairs) so closely with the spinal 

 nerves in most respects, that only a brief description of them is 

 here required. 



All these nerves, except the fifth pair (trigeminus), ninth (glosso- 

 pharyngeal), and tenth pair (pneumogastric), and perhaps the ele- 

 venth (spinal accessory) rise from a single root instead of two; 

 and are, therefore, exclusively motor or exclusively sensory. The 

 fifth pair is, however, historically and physiologically a spinal 

 nerve ; and for the description of its ganglion (the Gasserian), and 

 its final distribution, we refer to the spinal nerves. Several gan- 

 glia are, however, placed upon it (submaxillary, &c.), as upon the 

 sympathetic; and they present the same structure also as the latter, 

 except that they contain a considerable number of larger nerve, 

 cells. The ninth pair (glosso-pharyngeal), though endowed with 

 motor properties, has no fibres which do not pass through the one 

 or the other of its ganglia. Its ultimate ramifications in the tym- 

 panic cavity and in the tongue, contain small ganglia. The tenth 

 pair (pneumo-gastric) has all its roots enter the jugular ganglion 

 in man ; while in several lower animals (dog, cat, rabbit, &c.), it has 

 a primary fasciculus not connected with the ganglion. The latter 

 presents no peculiarity, except that the nerve-cells occasionally 

 measure only i-f^-g of an inch, though there are many as large as 

 _fa of an inch. The ultimate distribution of this nerve exhibits a 

 constant separation of thicker from more slender fibres; so that the 

 branches to the oesophagus, heart, and stomach are composed almost 

 entirely of fine fibres; while in those going to the lungs, and in 



