596 THE FUNCTION OF THE SPINAL CORD 



system of these animals to operative interferences. The profound 

 general reactions following these operations, are commonly centered in 

 the phenomenon of shock and the development of a hypersensitiveness 

 which frequently overshadows the primary effect. But while it must 

 be granted that the spinal cord of the higher animals does not exhibit 

 quite so decided a segmentalism as that of the reptiles, amphibia and 

 fish, it nevertheless evinces a decided tendency at locaUzation of func- 

 tion. Sherrington, 1 for example, has shown that the decapitated cat 

 reacts to stimulations of the skin either by scratching movements or 

 by flexion and extension of the legs. In fact, it is easily noted that a 

 decerebrated animal, or one in which merely a part of the cerebral 

 cortex has been removed, exhibits an even greater number of reflexes 

 than a normal animal. Quite similarly, the division of the spinal 

 cord at a point posterior to the nuclei of the phrenic nerves does not 

 materially affect the reflexes from the posterior extremities. The 

 patellar and other deep reflexes are not destroyed thereby. 



Besides these centers which are solely concerned with reactions 

 of skeletal muscle, it has been proved that the spinal cord also con- 

 tains centers for several reflex acts of different character, as follows: 



(a) Dilatation of the pupil. This center lies opposite the 1.-3. thoracic ver- 

 tebrae. The motor fibers leave by the anterior roots and enter the upper thoracic 

 nerves and the cervical sympathetic, terminating finally in the ganglion cervicale 

 superior. 



(6) The center for defecation, or centrum anospinale, is situated opposite 

 the fifth lumbar vertebra (dog). The afferent path is formed by the plexus 

 hemorrhoidalis and the efferent path by the nervus hypogastricus. 



(c) The center for micturition, or centrum vesicospinale, is situated in the 

 lumbar or sacral segment of the spinal cord. The nervi hypogastrici and erigentes 

 constitute the efferent path. 



(d) The centers for the erection of the male and female generative organs are 

 situated in the lumbar portion of the cord. The arteria profunda penis is inner- 

 vated by the vasomotor fibers of the 1.-3. sacral nerves, while the 3. and 4. sacral 

 nerves activate the muse, ischiocavernosus and transversus perinei profundus. 



{e) The center for ejaculation is also placed in the lumbar segment of the 

 cord. 



(f) The center for the contraction of the uterus is located in the lumbar seg- 

 ment of the cord. 



{g) The centers in the bulbar enlargement of the cord, i.e., in the medulla 

 oblongata, regulate the activity of the heart, the respiratory movements, the cali- 

 ber of the blood-vessels, deglutition, reversed deglutition or vomiting, heat dissi- 

 pation, and other functions. 



In view of this rather well marked segmentalism, it cannot be 

 denied that the spinal cord of the higher animals possesses a functional 

 arrangement very similar to that present in the lower forms. It is an 

 important seat of reflex action. But, inasmuch as the cerebrum gradu- 

 ally gains a more complete control over these simple functions, 

 the spinal centers lose their independency of action. This is especially 

 true of man, because, somewhat contrary to the results obtained in the 

 dog, cat and rabbit, the complete division of the spinal cord is followed 

 ^ Jour, of Physiol., xxxviii, 1909, 375. 



