THE ATLANTIC SLOPE NATURALIST. 



whilst the remainder of the canal 

 forms the spinal cord. The dilation 

 of the anterior half of the Canal is at 

 first uniform; this uniformity is very 

 shortly interrupted by the appearance 

 of two constrictions, which are simple 

 ingrowths of the lateral walls of the 

 Neural Canal at this point. These 

 constrictions divide the future brain 

 into three sacs or vesicles, the cavities 

 of these sacs being in broad communi- 

 cation with one another. These sacs 

 are known as the Primary Brain Ves- 

 icles, or as the fore- mid- and hind- 

 brain vesicles. This condition is very 

 shortly followed by the appearance of 

 two other infoldings, which divide the 

 three primary brain vesicles or sacs 

 into five vesicles or compartments — the 

 primary Fore-brain being divided into 

 the fore- and inter-brain vesicles, the 

 primary Hind-brain being divided into 

 the hind and after-brain vesicles, which 

 with the undivided Mid-brain Vesicle 

 constitute the five elementary brain 

 vesicles or sacs which will ultimately 

 form the entire adult brain structure. 



Up to the time of the completion of 

 the three vesicle stage of development, 

 the brain vesicles lie in a straight 

 line, one behind the other, with the 

 formation, however, of the five vesicle 

 stage, there takes place a change in 

 the relationship of the brain vesicles 

 with one another, which has an im- 

 portant bearing on the ultimate adult 

 condition. This change is the appear- 

 ance of a bend or flexure which brings 

 the fore- inter- and mid-brain vesicles 

 on a line which is at right angles to 

 the remaining vesicles. In following 

 out the subsequent development of the 

 brain it will be found that the parts 

 of the brain developed from the differ- 

 ent embryonic brain vesicles are thus 

 brought into the permanent position 

 occupied in the adult brain. 



From the fore-brain are developed 

 the Cerebral Hemispheres, enclosing 

 the Lateral Ventricles, the two hemi- 

 spheres are foreshadowed very early by 

 a constriction antero-posteriorly, and 



which bisects the fore-brain and di- 

 vides it into equal halves, into this 

 constriction a band of connective tissue 

 — which surrounds the Neural Canal — 

 grows, and forms the dividing band of 

 the hemispheres, namely the Falx 

 Cerebri. 



From the inter-brain vesicle are 

 formed all of the structures which 

 surround the cavity of the Third Ven- 

 tricle, the cavity itself being simply 

 that portion of the Neural Canal em- 

 braced by the inter-brain vesicle. From 

 the next succeeding vesicle — Mid-brain 

 Vesicle — are formed all of the brain 

 structures surrounding the Aqueduct of 

 Sylvius. From the Hind-brain Vesicle 

 are formed a part of the floor of the 

 Fourth Ventricle, together with the 

 Pons and Cerebellum, and from the 

 After-brain Vesicle the remainder of 

 the Fourth Ventricle and the Medulla 

 Oblongata are formed. 



The object of this article is simply 

 to give a brief description of the mor- 

 phological formation of the nervous 

 system, I will not, therefore, go into 

 a detailed description of the histologi- 

 cal changes that go hand in hand with 

 the grosser ones, I will simply add that 

 the Essential Nerve Constituents of the 

 brain and cord, are formed from the 

 epithelial elements composing the wall 

 of the embryonal neural canal, the 

 ventricles and the aqueduct of sylvius 

 simply being subdivisions of the cavity 

 originally contained in the neural 

 canal. 



WANTED: WORKERS IN SCIENCE. 

 The great need of science in this 

 country, we are told by a writer in 

 the Popular Scie?ice Monthly, is not 

 so much buildings or endowments, but 

 men. There are not nearly enough 

 workers to investigate properly all the 

 new objects, facts, and principles that 

 are coming to light every day. 

 Science has work cut out for the whole 

 lifetime of many more investigators 

 than are willing to devote themselves 

 to her cause. All of which means 



