FREE BOOKS

Author's List




PREV.   NEXT  
|<   118   119   120   121   122   123   124   125   126   127   128   129   130   131   132   133   134   135   136   137   138   139   140   141   142  
143   144   145   146   147   148   149   150   151   152   153   154   155   156   157   158   159   160   161   162   163   164   165   166   167   >>   >|  
ally belonging to it, may be mentioned the anterior lobes of the pituitary body; these begin as an upward _diverticulum_ from the posterior wall of the primitive pharynx or _stomatodaeum_ about the fourth week. This _pouch of Rathke_, as it is called, becomes nipped off by the developing base of the skull, and its bifid blind end meets and becomes applied to the posterior part of the body, which comes down from the brain. In the mesencephalon the alar laminae form the _corpora quadrigemina_; these at first are bigeminal and hollow as they are in the lower vertebrates. The basal laminae thicken to form the _crura cerebri_. In the rhombencephalon the division into basal and alar laminae is better marked than in any other part; there is a definite groove inside the fourth ventricle, which remains in the adult as the superior and inferior _fovea_ and which marks the separation between the two laminae. In the basal laminae are found the deep origins of most of the motor cranial nerves, while those of the sensory are situated in the alar laminae. The roof of the fourth ventricle widens out very much and remains largely epithelial as the superior and inferior medullary vela. The cerebellum develops in the anterior part of the roof of the rhombencephalon as two lateral rudiments which unite in the mid line and so form a transverse bar similar to that seen in the adult lamprey; at the end of the second month the flocculus and paraflocculus become marked, and later on a series of transverse fissures occur dividing the various lobes. Of the cerebellar peduncles the inferior develops first (third month), then the middle forming the _pons_ (fourth month), and lastly the _superior_ (fifth month) (Elliot Smith, _Review of Neurology and Psychiatry_, October 1903; W. Kuithan, "Die Entwicklung des Kleinhirns bei Saugetieren," _Munchener Med. Abhandl._, 1895; B. Stroud, "Mammalian cerebellum," _Journ. of Comp. Neurology_, 1895). Much of our knowledge of the tracts of fibres in the brain is due to the fact that they acquire their white sheaths at different stages of development, some long after birth. For further details and references see Quain's _Anat._ vol. i. (1908); Minot's _Human Embryology_ (New York); W. His, _Anat. menschlicher Embryonen_ (Leipzig, 1881); Marshall's _Vertebrate Embryology_; Kolliker, _Grundriss der Entwickelungsgeschichte_ (Leipzig, 1880); A.
PREV.   NEXT  
|<   118   119   120   121   122   123   124   125   126   127   128   129   130   131   132   133   134   135   136   137   138   139   140   141   142  
143   144   145   146   147   148   149   150   151   152   153   154   155   156   157   158   159   160   161   162   163   164   165   166   167   >>   >|  



Top keywords:
laminae
 

fourth

 

superior

 

inferior

 

cerebellum

 
develops
 
transverse
 

Neurology

 
ventricle
 

marked


remains

 

rhombencephalon

 
Embryology
 

anterior

 
posterior
 

Leipzig

 
October
 
Psychiatry
 

Grundriss

 

Review


Kuithan

 

Saugetieren

 

Munchener

 

Kolliker

 

Entwicklung

 

Kleinhirns

 

fissures

 

dividing

 

series

 

cerebellar


middle

 
forming
 

lastly

 

peduncles

 

Entwickelungsgeschichte

 
Elliot
 

Abhandl

 
stages
 

sheaths

 
development

references
 

paraflocculus

 
Mammalian
 
Stroud
 

Marshall

 

details

 
knowledge
 

acquire

 
menschlicher
 

Embryonen