TOG 



THE XER VOL'S SYSTEM 



covered l)y epithelium for the anterior two-thirds or tliree-fourths of its extent, and 

 hounds in' part the cavity of the third ventricle. Its inferior surface rests in the 

 mesial groove between the su})eri(tr (juadrigeminal l)odies, separated from the latter 

 by a fold of ])ia mater. The stalk of the pineal body is continuous Ijy its lower 

 lamina with the ])()sterior commissure. Its upper lamina passes into the peduncle 

 or stria pinealis, which passes at first outwards, and then forwards, along the 

 margin of the optic thalamus which separates the upper and mesial surfaces of that 

 bodv; it then crosses the flocn- of th(.' foramen of Monro and joins the anterior 

 pillars of the fornix. 



The recessus pinealis is a diverticulum from the cavity of the third ventricle, ■whicli extends 

 into the stalk and a short distance into the body of the conarium. "Within the pineal body, and 

 in the adjacent part of the velum interpositum, a number of gritty particles (acervulus cerebri, 

 i)rain sand) are found. These particles consist chiefly of phosphate and carbonate of calcium. 

 The pineal body was formerly described as a gland (pineal gland) but is now known to be a 

 rudimentary unpaired eye. This pineal eye lies close to the surface in some of the lower verte- 



FiG. 4-22. — CoKox.4L Sectiox theough the Middle Commissure of the Third 

 Ventricle. (Schwalbe.) 



CORPUS 

 CALLOSL'Jf 



THIRD 



VENTRICLE 



INNER 



CAPSULE 



OPTIC TRACT 



LA TERA L 

 VENTRICLE 



TAENIA SEMI- 

 CIRCriARIS 



LENTKTLAR 

 NUCLEUS 



OUTER CAPSULE 

 .MIDDLE 



COMMISSURE 

 ISLAND OF REIL 

 (LAUSTRUM 



AMYGDALOID 

 NUCLEUS 



brates, and was proljably functional at a former period. A great i)arietal foramen in the extinct 

 reptile Ichthyosaurus is strongly suggestive of a functional pineal eye. 



The posterior commissure is a transverse hand of fibres which projects into 

 the posterior part of the cavity of the third ventricle (page 708). 



The subthalamic tegmental regitjn and the corpora geniculata will be more conveniently 

 described with the mesejicei)halon. 



The basal grey commissure is a continuous plate of grey matter wliich is 

 formed from behind forwards by the posterior perforated space, the tuber cinereum, 

 and the lamina cinerca. 



The posterior perforated space is a stratum of grey matter which is perforated 

 by a numl)er of small vessels thrived from the commencements of the posterior 

 cerebral and superior cerebellar arteries. It occujiies the back part of the inter- 

 pediuicular space and extends for a short distance under cover of the pons, where it 

 bounds a recess, the foramen caecum anterius. It is cc^ntinuous laterally with the 



