88 



ANATOMY OF THE HEAD AND NECK. 



separated by the septum lucidum from its fellow of tl 

 opposite side; its narrow end projects backward outsi( 

 the optic thalamus. 



The tsenia semicircular is is a narrow band of 1( 

 tudinal fibres, lying between the corpus striatum and the 

 optic thalamus; in front it joins the pillar of the fornb 

 and posteriorly is lost in the descending cornu of the 

 ventricle. 



The optic thalamus is an oblong body, a part of the uppei 

 surface of which is alone seen, the rest being covered 

 the fornix ; its posterior portion projects into the descent 

 ing cornu of the ventricle; its other relations will be sul 

 sequently examined. 



The choroid plexus is a vascular fringe, formed from the 

 pia mater, which extends obliquely across the ventricle 

 posteriorly it penetrates into the descending cornn, am 

 anteriorly it communicates with the plexus of the othei 

 side through the space behind the crura of the fornix 

 they arch downward, called theforamenofMonro, and this 

 may be demonstrated by pulling the plexus gently with 

 pair of forceps, while the septum lucidum is held aside b 

 the handle of a scalpel. 



The hippocampus major is the projection which lies at 

 the commencement of the descending cornu, behind the 

 choroid plexus ; it follows the direction of the cornu, an< 

 its extremity has been likened to the foot of an animal, the 

 two or three indentations, with corresponding elevations, 

 which are found upon it having been named pes hippocampi. 

 In order to see this, the cornu must be laid open by a can 

 ful division of the external wall of the hemisphere, follow- 

 ing a direction backward, outward, and downward, an< 

 then forward and inw^ard. The primary letters of th( 

 words used to express the curve taken by the cornu hav( 

 given rise to a mnemonic symbol, BODFI, by which the sti 

 dent may with ease remember its course. 



The hippocampus minor is the projection which occupies 

 nearly all the space of the posterior cornu. Between th< 

 two hippocampi is an elevation called the eminentia colic 

 teralis. 



The corpus callosum is to be out through transversely at its middle : 

 the anterior half is to be raised by separating it from the fornix am 

 reflected forward ; this exposes the septum lucidum and its ventricle. 

 The posterior half is to be raised and reflected backward ; the forni: 

 will thus be exposed. 



