284 THE RHOMBENCEPHALON. 



the medial fillet be destroyed and not the spino-thalamic and 

 anterior ascending cerebello-spinal tracts, then the pain and 

 temperature sense is intact, but the muscular sense is lost on the 

 opposite side of the body. The tactile sense is impaired in both 

 cases. A lesion of the trapezoid body produces almost total 

 deafness; of the lateral fillet, slightly impaired hearing on the 

 same side and nearly complete deafness in the opposite ear. 

 Conjugate deviation occurs when the nucleus of the sixth nerve 

 is affected; and strabismus when the root fibers, but not the 

 nucleus, are involved. The strabismus is external if the lesion 

 be irritative and internal if the root fibers are destroyed. Des- 

 tructive lesion in the nucleus of the seventh nerve causes inferior 

 paralysis of the face, the frontalis, corrugator, orbicularis oculi 

 and orbicularis oris not being affected. Complete facial paral- 

 ysis occurs if the root-fibers of the facial nerve be destroyed in 

 the pars secunda or in the genu internum. 



RHOMBENCEPHALON. 



SECTION III. THE MEDULLA OBLONGATA. 

 (MYELENCEPHALON.) 



Situation. The medulla oblongata is the distal, or caudal 

 part of the brain (Figs. 21 and 27). It may be regarded as the 

 expanded intra-cranial portion of the spinal cord, hence the 

 synonym, spinal bulb. It occupies the basilar groove of the 

 occipital bone, posterior to the pons; and is continuous with the 

 spinal cord below the foramen magnum. Dorsally, it is in part 

 concealed in the valley of the cerebellum. The vertebral arteries 

 wind forward around it, and form the basilar at its junction with 

 the pons. 



Size. The medulla is about an inch long, and dorso-ventrally, 

 is a half-inch thick. Its width at the lower end is a half-inch, also. 

 At the upper extremity it measures from three-quarters of an 

 inch to one inch in width (Figs. 85 and 86). 



Its shape resembles an inverted frustum of a cone flattened 

 dorso-ventrally at the base. The truncated apex of the frustum, 

 which is nearly circular in outline, is continuous with the spinal 



