674 FUNCTIONS OF THE CEREBRO-SPINAL NERVOUS SYSTEM. 



FIG. 241. 



invested in a very peculiar manner by vesicular substance, and of a central 

 lobe, also containing a combination of the vesicular and fibrous substances, 

 which is known under the designation of the " vermiform process." The 

 hemispheres are connected with each other not only by this central lobe, but 

 also by the fibrous commissure which passes beneath the Medulla Oblongata, 

 and is known as the " Pons Varolii." The commissural fibres form part of 



the "Crura Cerebelli;" but another portion 

 is formed by the strands which c'ounect the 

 Cerebellum with the anterior and posterior 

 columns of the Spinal Cord and Medulla Ob- 

 longata ( 488); and in addition to these, we 

 find a fasciculus of fibres passing between the 

 Cerebellum and the Corpora Quadrigemina, 

 the "iter a cerebello ad testes." The peduncle 

 of its hemispheres on either side contains a 

 mass of gray matter, the "corpus rhomboi- 

 deum," or, "dentatum," which seems to be a 

 gauglionic centre for the fibres that pass up- 

 wards to it from the Spinal Cord. There are, 

 then, three masses of gray matter in the cere- 

 bellum that of the cortex, the dentated nu- 

 clei, and the roof-nuclei of Stilling, situated 

 in the medulla of the Vermiform process. 

 The accompanying figure (Fig. 241) exhibits 

 the appearance presented when a section of 



Transparent section from me cortex of .-, /> ,1 n i n j 



the cerebellum of Man. the cortex of the Cerebellum is examined, 



i a. External portion of the pure gray and it will be seen that it differs consider- 



layer. ably from that of the Cerebrum given on p. 



1 6. Internal portion of the pure gray 69Q. 1 The inquiries of Eugel 2 have sho\Vll 



layer with fusiform cells and fibra; arcu- that t])e development of the Cerebellum is 

 "T The layer of Purkinje's ceils. completed in infancy, and remains unaltered 



3. The layer of grannies. U P to the 50th year, after which the number 



m. Medullary lamina. of the lamella;, especially of the superior ver- 



miform process, begin to diminish. 



547. When we examine into the relative development of the Cerebellum 

 in the different classes of Vertebrata, we find that it presents some very re- 

 markable differences. 3 In its simpler forms, this organ is found to consist 

 entirely of the representative of the central lobe of the Human Cerebellum, 

 the hemispheres not making their appearance until we have ascended to the 

 class of Birds. On ascending the scale of Mammiferous animals, on the 

 other hand, we cannot but be struck with the rapid advance in the propor- 

 tional si/e of the Cerebellum, which we observe as we rise from the lowest 

 (which arc surpassed in this respect by many Birds), towards Man, in whom 

 it attains a development which appears enormous, even when contrasted with 

 that of the (^uadrumana. In proportion, in fact, as the extremities acquire 

 the power of prehension, and together with this a power of application to a 



1 For an admirable description of the Human Cerebellum, see Stilling'* Kssay on 

 tin- Structure of tlic Organ. Cassol, 1S()7. Also Deiter's Un tor-such, ill). Gchirn. v. 

 Euckciimark, ISilo; M eynert, in Strieker's Hum. and Comp. Histology, vol. ii, 1872, 

 p. 512; Hadlich, Arehiv f. Microscop. Anat., Bd. vi, p. 1'Jl. 



AVien. Mrdi/.in. Wochens., 18IJ3, No. 33. 



3 Sec 1'rine. ol' Comp. Phys., \ 635. Fuller information on this point will lie found 

 in M. Serres's Anat. Comp. du Cerveaii, and M. Leuret's Anat. Comp. du Hy.-leme 

 Nervcux. For ; , general discussion of the evidence afforded by Comparative Anatomy 

 in regard to th<> functions of the Cerebellum, sec the Brit, and For. Aicd. Rev., vol. 

 xxii, pp. 5:55-541. 



