382 



HEALTH AND DISEASE 



of the comma -like bodies are named the cornu, and there are conse- 

 quently an upper and a lower cornu on each side. The upper one is 

 more pointed, and reaches nearer to the surface than the lower cornu. 

 The isthmus or central portion, which joins the two lateral masses of 

 gray substance, is perforated by a small hole, which represents the section 

 of a tube, named the central canal, which runs the whole length of the 



cord. If the nerve roots be traced 

 into the substance of the cord, it 

 will be found that the fibres of 

 which they are composed chiefly 

 end in branches surrounding the 

 nerve -cells of the superior and 

 inferior" cornu of their own side, 

 whilst some ascend towards the 

 brain on that side, and others 

 cross over to the opposite side. 

 Each half of the white substance 

 of the cord is obviously divided 

 into three regions: 1, an upper, 

 between the superior cornu and 

 the superior median fissure; 2, a 

 lateral, between the upper and 

 lower cornu; and 3, a lower region, 

 between the inferior cornu and 

 the inferior median fissure. 



Fig. 174.-Under Surface of Horse's Brain J n g()me i nstance s the fibres 



A Temporal Lobe B Crura Cerebri. c Pons constituting these divisions COn 



Varolu. D, Medulla Oblongata. E, Cerebellum. 



F, F, Convolutions of Cerebrum. I, Olfactory Nerve or 1st 

 Nerve. n, Optic Nerve or 2nd Nerve. Ill, Motores 

 Occulorum or 3rd Nerve. IV, Pathetici or 4th Nerve. 



v, Trifacial or 5th Nerve, vr, Abducent Nerve, vn, Facial chiefly made UD of SCnSOlT 

 or 7th Nerve. vin, Auditory or 8th Nerve. IX, Glosso- . J J 



pharyngeal or 9th Nerve. x, Pneumogastric or 10th whilst Others are essentially motor. 

 Nerve. xi, Spinal Accessory or llth Nerve. xii, Hypo- f)^ HV*\T\ rp rn\Wf\ flTlH rnn 

 glossal or 12th Nerve. efS a g am are miXCd, ana C 



vey impulses both upwards to the 



medulla oblongata, cerebrum, and cerebellum, and downwards from these 

 centres to the muscles. 



The Bulb, or Medulla Oblongata. This portion of the nervous 

 system (D, fig. 174) occupies a position intermediate between the spinal 

 cord and the pons (c, fig. 174), and is continuous with both. It forms 

 a kind of capital to the cord, and possesses a highly intricate structure. 



It is the seat of origin of some of the most important nerves in the 

 body, particularly of those which confer sensibility upon the face and 



Vs 



duct impressions forwards, in 

 others backwards. Some are 



