THE BACK. 411 



horns respectively of the spinal cord ; (3) the ganglion on the sensory root of 

 the fifth cranial nerve and the ganglion on the root of the vagus are homologous 

 to the ganglia on the posterior roots of the spinal nerves ; (4) cases are recorded 

 of absence of the ganglion on the posterior root of the first spinal or suboccipital 

 nerve ; (5) cases are recorded of the hypoglossal the twelfth cranial nerve 

 having a posterior root with a ganglion. Possibly anomalous cases like those 

 cited in 4 and 5 may account for and even justify the tenth cranial nerve the 

 hypoglossal in the classification by Willis. 



In iv hat respects do spinal nerves differ from cranial nerves / 



In the following respects : (i) Spinals arise from the spinal cord ; (2) spinals 

 have an anterior motor and a posterior sensory root ; (3) spinals have a ganglion 

 on each posterior root ; (4) spinals have no special sense nerves. 



State where the ganglia of the posterior or sensory roots of the spinal nerves may 

 be found in dissecting. 



The rule is that these ganglia occupy the posterior root of the spinal nerve, 

 just behind the union of the anterior and posterior roots, in the intervertebral 

 foramen. 



Are there any exceptions to the rule governing the location of the spinal 

 ganglion / 



Yes ; the ganglia of the first and second cervical nerves lie on the neural 

 arches of the atlas and axis. The ganglia of the sacral and coccygeal nerves 

 are in the spinal canal. 



Describe the vagus or pneumogastric nerve. 



This nerve is the tenth cranial, according to the classification of Soemmering ; 

 it is also called the nervus vagus and the nervus par vagam. The nerve leaves 

 the base of the cranium by the central part of the jugular foramen with the spinal 

 accessory and glosso-pharyngeal nerves. 



Where is the ganglion of the root of the vagus located, and to what does it corre- 

 spond morphologically ? 



It is located in the jugular foramen, and corresponds to the spinal ganglion on 

 the posterior roots of the spinal nerves. 



What is the importance of the ganglion of the root of the vagus nerve ? 



It has connections with the sympathetic, spinal accessory, glosso-pharyngeal, 

 and facial nerves. (Fig. 293.) 



Where is the ganglion of the trunk of the vagus nerve and ivliat its impor- 

 tance ? 



It is a little below the ganglion of the root and below the base of the skull. 

 Its importance is due to the fact that branches are given off from it to the sympa- 

 thetic, to the cervical nerves, and to the hypoglossal nerve ; also the accessory 

 part of the spinal accessory nerve joins the vagus at this point. (Fig. 293.) 



Describe the olfactory nerve. 



The olfactory nerve, as generally understood, is in reality a dismembered part 

 of the fore-brain of the foetus. It consists of four parts, as may be appreciated by 

 consulting figure 286. 



1. The olfactory roots, three in number. 



2. The olfactory tract, a slender bundle. 



3. The olfactory bulb, resting on the cribrosa. 



4. The olfactory filaments, about twenty in number. 

 Name and give the source of the olfactory roots. 



The middle root is attached to the under surface of the frontal lobe ; the 

 internal root to the gyrus fornicatus ; the external root to the temporo-sphenoidal 

 lobe. The roots meet to form the olfactory tract. The tract becomes bulbous 

 and occupies a fissure on the under surface of the frontal lobe of the cerebrum, 

 called the olfactory sulcus. The olfactory nerves are given off from the under 



