422 ANATOMY AND PHYSIOLOGY OF THE BRAIN. 



respiratory process. To effect an inspiration, a very com- 

 plex series of actions are brought about ; thus, the muscles 

 of the nostrils and cheeks must be acted on by the facial 

 nerve, the larynx opened by the pneumogastric, the dia- 

 phragm contracted by the phrenic, which leaves the spinal 

 cord at the fifth and sixth segments of the backbone, and 

 the muscles of the trunk thrown into action by the spinal 

 nerves in the region of the back, before a satisfactory in- 

 spiration can be brought about. This is not all, however. 

 The action of all the muscles implicated must be simulta- 

 neous, not only with each other, but especially so with 

 those of the opposite side, and a perfect harmony must 

 exist as to force and duration of impression. According to 

 Van der Kolk, the various nuclei of these nerves are inti- 

 mately connected with each other by nerve-fibres, and 

 those on the two sides are similarly connected through the 

 numerous transverse fibres that exist in the substance of 

 the medulla. He holds, moreover, with Sir Charles Bell 

 and Schiff, that the lateral columns of the cord preside espe- 

 cially over the respiratory movements of the trunk, and 

 that as these terminate in nuclei close to the origin of the 

 pneumogastric nerve, the intimate connection of movement 

 between these and the others referred to is easily under- 

 stood. Here, then, as in the spinal cord, are groups of 

 ganglionic cells, forming the origins of different nervous 

 trunks, and so intimately connected by intervening fibres, 

 that under a single impulse they lead to a harmonious action 

 of muscles situated in widely different parts of the body. 



The impression which leads to the respiratory process 

 seems conveyed principally from the lungs through the 

 pneumogastric nerve, and results from the presence, in the 

 pulmonary capillaries, of blood charged with carbonic acid. 

 The extensive connections of the oblong medulla, how- 



