ZOOLOGICAL 1>BJ-' U 

 CORNELL UNiVLRi.''*' 



JTHACA N- >'■ 

 THE MAMMALIAN NERVOUS "SYSTEM 65 



endings in the skin, subcutaneous tissues, muscle spindles, ten- 

 dons, joints, etc. See Herrick ('15), Chap. V; Barker ('01), pp. 

 361-421; Sheldon ('18), Chap. XXIV; and all works on histology, 

 (b) Now review again the superficial landmarks of the ventric- 

 ular and lateral surfaces of the human medulla oblongata, with 

 special reference to the underlying functional columns (see Sec- 

 tions 51 to 57). General somatic sensory fibers for cutaneous 

 and deep sensibility of the head are found in the V, IX, and X 

 cranial nerves (Herrick ('15), Chap. XI), and the special 

 somatic cochlear (Herrick ('15), Chap. XIII) and vestibular 

 (Herrick ('15), Chap. XII) are represented in the VIII nerve. 

 The connections of these systems will next be taken up, together 

 with the cerebral portions of the spino-cerebral tracts whose 

 spinal parts have already been mentioned. The cerebellum, 

 which is a derivative of the somatic sensory column, will be ex- 

 amined later, and the composition of its peduncles summarized. 



71. The general cutaneous system. — The cutaneous fibers from 

 the face enter the brain by the V nerve; a smaller number by 

 the IX and X nerves. The fibers of the sensory V root in part 

 end in the chief sensory V nucleus dorso-medially of the super- 

 ficial origin of the root, but most of them turn abruptly spinal- 

 ward and thus form the spinal V tract, whose fibers form an 

 eminence on the lateral surface of the oblongata — the tuber- 

 culum cinereum or tubercle of Rolando. 



72. Gross preparation of the spinal V tract. — On the right half 

 of the brain of the sheep locate the V, IX, and X roots (Figs. 7, 8, 

 12) and the tuberculum cinereum. Now with a wooden dissec- 

 tor begin at the lower border of the V root and carefully scrape 

 away the transverse fibers of the pons and the trapezoid body 

 until the longitudinal fibers of the spinal V tract lying im- 

 mediately internal to them are exposed. Continue the dis- 

 section spinalward by gently teasing off the superficial external 

 arcuate fibers (see Section 90). Careful scraping in the longi- 

 tudinal direction with an orange-wood stick sharpened to a 

 slightly rounded chisel edge will readily expose the whole length 

 of the spinal V tract to its terminus in the cervical cord. In its 

 spinal course its fibers become superficial. 



A similar dissection can readily be made on the human brain 

 also, though the larger size of the pons makes it necessary to cut 

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