l88 FUNCTIONS OF THE BRAIN. 



The Nerve-muscle Chewing Apparatus. — The leg movement in chewing 

 is produced by two muscles, a flexor and an extensor, both innervated by a branch 

 of the pedal nerve. (Fig. 114, ex"^ and^l) The motor nerve-ceUs of these mus- 

 cles while not certainly located probably lie in, or close to, the pedal ganglion, Al 



The jaw movement is controlled by nine muscles. The "in" movement is 

 produced by four plastro coxals, pi. ex., two in front, and two behind, going from 

 the edge of the plastron to the sides of the coxae; the "out" movement by the five 

 coxo-tergals, cx.t., two in front and three behind, extending from the base of the 

 coxa to the dorsal shield. These nine muscles are innervated by the anterior 

 and posterior ento-coxal nerves, a. en. ex. and p. en. ex. that spring from the clusters 

 of motor cells lying on the haemal side of the brain, one on each side of the pedal 

 ganglion. (Fig. 66, H.) Each of these motor cells gives off numerous fibers to the 

 ento-coxal muscles; to the crus of the same side, and to the opposite crus, through 

 the corresponding commissure. (Fig. 114, h.) 



Experimental Results. — The results obtained by cutting the collar at various 

 places are naturally not always intelligible, but when they are they appear to be 

 in harmony with the anatomical relations just described. These results are as 

 follows: 



I. Cutting the posterior end of one crus, or of both crura, behind, or close 

 to the sixth thoracic neuromere does not materially affect the chewing reflexes. 

 2. Cutting across one crus close to the hemispheres, produces increased vigor, and 

 a diminished coordination in the chewing movements of the legs on the cut side. 

 The jaw movement is either unmodified or slightly diminished. If both crura 

 are cut, the above results are obtained on both sides. These operations not only 

 separate the hemispheres, but the main gustatory and swallowing centers from 

 the thoracic neuromeres. The results point to the presence of separate control- 

 ling centers on each side of the forebrain. 3. An isolated segment of the collar, 

 containing one or two neuromeres, lying between the second and sixth neuromeres, 

 and separated from the opposite side by cutting its cross commissures, may give 

 feeble, uncoordinated, gustatory reflexes, but such an isolated portion of the collar 

 generally degenerated and soon failed to give further response. 4. However, in 

 experiment III — B, the left side of the collarwas completely isolated and lived with- 

 out perceptible degeneration for three weeks. But this segment undoubtedly in- 

 cluded that part of the cheliceral neuromere containing the secondary gusta- 

 tory center and the swahowing center, and only a small part, if any, of the 

 hemisphere. This segment readily produced the chewing reflexes; the reflexes 

 were normal except for the exaggerated and uncoordinated leg movements on 

 the isolated side, and the lack of harmony between the chewing movements on 

 the one side with those on the other. The results show : a. that the coordination 

 and inhibition of the leg movements on the one side he in the hemisphere of the 

 same side, probably in the large median lobe, or tertiary gustatory center; b. that 

 the rhythmic control of the chewing movements of one side is located in the second- 

 ary gustatory center in the cheliceral neuromere; and e. that the coordination of 



