FIVE TRIMARY DIVISIONS OF THE BEAIN. 



753 



There are thus distinguished the rudiments of five fundamental 

 constituents of the brain, under which it will be found convenient to 

 bring the notice of the development of the several parts forming the 

 full grown organ, and which m^y in this association be shortly enume- 

 rated as follows, viz. : — 



1. The cerebral hemispheres, with their ventricular hollows or lateral 

 ventricles, the corpora striata, and the olfactory lobes, — a set of parts 

 to which, as a whole, the name of proceredrum or j)rosejice2}haIo?i may be 

 Q-iveu. 



Fig. 554. — Sketches of the early form Fig. 554. 



OF THE PARTS OF THE CeREBRO-SPINAIi 



Axis in the Human Embryo (after '*- 



Tiedemann). 



A, at the seventh week, lateral view ; 



1, spinal cord ; 2, medulla oblongata ; 3, 

 cerebellum ; 4, mesencej^halon ; 5, 6, 7, 

 cerebrum. B, at the ninth week, pos- 

 terior view; 1, medulla oblongata; 2, 

 cerebellum ; 3, mesencephalon ; 4, 5, tlia- 

 lami optici and cerebral hemispheres. 

 C and D, lateral and posterior views of 

 the brain of the human embryo at twelve 

 weeks, a, cerebrum ; b, corpora quadri- 

 gemina ; c, cerebellum ; d, medulla ob- 

 longata ; the thalami are now covered by 

 the enlarged hemispheres. E, posterior 

 view of the same brain dissected to show 

 the deeper parts. 1, medulla oblongata ; 



2, cereliellum ; 3, corjDora quadrigemina ; 

 4, thalami optici ; 5, the hemisphere tuined 

 aside ; 6, the corpus striatum embedded 

 in the hemisphere ; 7, the commencement 

 of the aorpus callosum. F, the inner side 

 of the right half of the same brain sepa- 

 rated by a vertical median section, show- 

 ing the central or ventricular cavity. 1, 2, 

 the spinal cord and medulla oblongata, 

 still hollow ; 3, bend at which the pons 

 Varolii is formed ; 4, cerebellum ; 5, lamina 

 (supierior cerebellar peduncles) passing up 

 to the corpora quadrigemina ; 6, crura 

 cerebri ; 7, corpora quadrigemina, still 

 hollow ; 8, third ventricle ; 9, infundibu- 



lum ; 10, thalamus, now solid ; 11, optic nerve ; 12, aperture leading into the 1 

 ventricle ; 13, commencing corpus callosum. 



F 



Literal 



2. The tlialamencephalon with its cavity or third ventricle, the 

 primary ocular pedicles, and the infundibulum. 



3. The mcsenceplialon, which is the same with the original middle 

 vesicle, and comprises the corpora quadrigemina and crura cerebri with 

 its contracted internal hollow, the iter a tertio ad quartuni ventriculum 

 of human anatomy. 



4. The next part in succession is the cerehellimi, along with which 

 is included the pons Varolii and the fourth ventricle. 



5. The hinder part, which passes into the spinal marrow, is the 

 medulla oblongata, with the continuation of the medullary cavity in 

 the fourth ventricle and into the central spinal canal. 



In these five fundamental parts or rudiments of the brain, arising out 



VOL. II. 3 c 



