MAMMALIA. 



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origin of the auditory nerves are nearly the same as in man. The ventricular cords 

 forming the floor or surface of the fourth ventricle constitute the sensitive centres. 

 They are partially separated by a furrow. When the epithelial covering has been 

 removed, transverse bundles of fibres are observed, which meet at the furrow. When 

 the anterior parts or those attached to the ventricular cords have been removed, the 

 superficial furrow is found to form a decided ridge. The structure of this surface 

 consists of transverse bundles of fibres intersected by longitudinal ones, so that the 







interstices form numerous pits for containing gray matter, affording some resemblance 

 a honeycomb. This structure is continued through the base of the quadrigeminal 

 bodies and the commencement of the sensitive tracts, the thalamus, and optic tracts. 

 At the ridge in the median line the transverse fibres meet, and communicate and 

 probably form a connection somewhat similar to the optic commissure. This structure 

 may be well seen in the oblong medulla of a large animal, and particularly that of 

 the ox. 



The involuntary centre is placed between the anterior and posterior surfaces of the 

 oblong medulla ; with which it corresponds, inasmuch as it is broader and thinner in 

 the horse and narrower and thicker in the ox and man : after sending a slip into the 

 spinal cord at the bottom of the anterior fissure, and giving origin to the accessory 

 nerve, the par vagum, the glosso-pharyngeal, and half of the larger portion of the fifth 

 nerve, it divides upwards into two portions, to pass underneath the thalami to their 

 appropriate convolutions. 



The restiform body is composed of an external and internal portion : the external, 

 which is a thinner layer, is continuous with the sensitive centre on the surface of the 

 fourth ventricle, and on being raised from the internal portion carries with it part of 

 the origin of the auditory nerve, so that it forms an extension of the sensitive centre, 

 and has the same cellular appearance. The more internal or thicker portion is the 

 true continuation of the first section of the median layer of the exterior region and 

 the anterior pedicle of the cerebellum, and of the third section of the exterior layer 

 with the posterior pedicle of the cerebellum ; it forms horizontal fibres, which leave 

 spaces between them for the issue of nervous roots and bloodvessels ; these fibres then 



