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medulla oblongata, which is the prolongation of the spinal cord. 

 It is globular in shape, its transverse diameter being the. greater. 



The membranes of the brain are the Dura Mater, Arachnoid, 

 and the Pia Mater. The dura mater is the thick, white fibrous 

 membrane which lines the cavity of the cranium, acting as the 

 internal periosteum of the bones. The middle one, called the 

 arachnoid, is a serous membrane of the ordinary character. The 

 pia mater is closely adherent to the entire surface of the brain, 

 dipping into every fissure or depression, into the sulci between 

 the convolutions, and passing into the interior in several places. 



The human brain exceeds, in comparative bulk, that of the 

 dog, the horse, or the ox. Thus are they classed in the order of 

 intelligence. The human brain weighs, on an average, 50 ounces. 

 The average weight of the horse's brain is 23 ounces. From the 

 medullary substance proceed nerves by which the animal is 

 enabled to receive impressions from surrounding objects, and 

 also to experience many pleasurable or painful sensations. One 

 of them goes to the nose, and gives the special sensation of 

 smell; another to the eye, and sight is produced; another to the 

 ear, and the animal is conscious of sound; another to the tongue, 

 and the taste is produced. Other nerves, proceeding to different 

 parts, stimulate the faculty of motion; others stimulate the sense 

 of feeling. Xerves which have their centers in the medulla 

 supply the respiratory organs, and the horse breathes. The 

 vasomotor center is the center of the sympathetic system sup- 

 plied to the muscular fiber of the blood vessels. They go to the 

 stomach, and it digests; to the heart, and it beats; to the oeso- 

 phagus and pharynx, and deglutition is performed; to the vocal 

 chords, and voice is produced; to the mouth, and mastication is 

 performed; to the salivary glands, and saliva is secreted. All 

 of these have their centers in the medulla. 



The muscles of the body are kept in a constant state of con- 

 traction or relaxation by nerve centers in the spinal cord. The 

 centers for micturation and defsrcation appear to exist in the 

 lumbar region of the spinal cord. The centers that govern the 



