THE HORSE. 



177 



of gangliform tubercles, from which ramifi- 

 cations proceed forward, as well as filaments 

 backward, to the ganglia of the nerves of 

 the medulla spinalis. It is considered gen- 

 erally as beginning from a branch of the 

 fifth and sixth pair, given off" at the base of 

 the cranium. The ganglionic structures 

 and the different plexuses are named from 

 their form, location, and distribution ; hence 

 we have the cervical ganglion, semilunar, 

 sacral, etc. From the semilunar ganglion 

 nervous filaments shoot in various direc- 

 tions, which, from their being compared to 

 the rays of the sun, are denominated the 

 solar plexus. From the divergent filaments 

 of the latter, the several smaller plexuses 

 of the abdomen may be said to derive 

 their formation, taking names according to 

 the viscera they are particularly designed to 

 furnish with nerves ; hence we have the 

 splenic plexus, that sends filaments to the 



spleen, the hepatic plexus, mesenteric, aortic, 

 hypogastric, and renal plexuses. The sym- 

 pathetic nerve in the abdomen travels over 

 the sides of the bodies of the lumbar verte- 

 brae, below the articulations of the ribs, and 

 pursues its course into the pelvis. Here, 

 also, it forms ganglia, which correspond in 

 number to those of the lumbar nerves : and 

 from every ganglion come off two filaments : 

 one which runs to the corresponding lumbar 

 nerve ; the other crosses the aorta, and, by 

 joining the aortic plexus, communicates 

 with nerves coming from the sympathetic 

 of the other side. 



From the loins, the sympathetic descends 

 into the pelvis, and takes its course along 

 the side of the sacrum, and forms five gan- 

 glia, corresponding to the sacral nerves ; it 

 finally terminates by forming a union with 

 its fellow. 



EXAMINATIONS ON NEUROLOGY. 



Examinations on Neurology, which will include the 

 names of parts not alluded to in the preceding 

 summary of the nervous system. 



Q. What are nerves ? — A. Long, firm, and white 

 chords, which ramify after the manner of blood-vessels, 

 and are distributed to all parts of the horse's body. 



Q. Where do they arise? — A. From the brain, 

 medulla oblongata, and medulla spinalis. 



Q. AVhat communications have the chfFerent nerves 

 with each other? — A. They anastomose : forming 

 sometimes a plexus; at others, a knot or ganglion, 

 from which other branches arise. 



Q. What is the structure of nerves? — A. They 

 consist of fasciculi, or bundles, of distinct longitudinal 

 fibres, closely connected together by cellular substance. 



Q. What are the coverings of nerves ? — A. Contm- 

 uations of those which envelop the brain and spinal 

 marrow, termed neurilema. 



Q. What is the structm-e of ganglions ? — A. They 

 are formed by a close intermixtiu-e of filaments. 



BRAIN AND ITS MEMBRANES. 



Q. Where is the brain situated? — A. It occupies 

 the cranial cavity. 



Q. How is the brain diA-ided ? — A. Into cerebrum, 

 cerebellum, and medulla oblongata. 



Q. By what membranes is the brain enveloped ? — 

 A. By three membranes, or meninges: 1st, The dura 

 mater ; 2d, Pia mater ; 3d, tunica arachnoides. 

 23 



DURA MATER. 



Q. What is the situation of the dura mater ? — A. 

 It is the external covering of the braui. 



Q. How does it differ from the other coverings of the 

 brain ? — A. It is more dense, tough, and inelastic. 



Q. How is it retained within the cranium ? — A. It 

 is fii'mly adherent to the interior of the cranium, more 

 particularly to the depressions between the teeth of the 

 cranial sutures. 



Q. How does the internal differ from the external 

 surface ? — A. It has a smooth, poUshed, and lubricated 

 surface. 



Q. Is the dura mater suppHed with nerves? — A. 

 Being composed of tendinous fibre, it is supposed to be 

 destitute of nerves. 



Q. How are the processes of the dura mater- 

 formed ? — A. By dupHcatiu*es. 



Q. What are the use of the processes ? — A. They 

 steady and protect the various divisions of the brain. 



Q. By what names are the processes known ? — A. 

 The longitudinal process is called falx cerebri, and the 

 transverse ditto is called tentorium. 



Q. What is the situation of the falx cerebri ? — A. 

 It forms a partition under the anterior and superior 

 parts of the cranial cavity extending from the crista 

 galU to the occiput, and ends in continuity with the 

 tentorium. 



Q. What is the situation of the tentorium cerebelli ? 

 — A. It is extended, after the manner of an arch, from 

 the cerebral plate of the occipitis along the sides of 



