274 



Anatomy of the Rabbit. 



By pressing apart the tips of the hemispheres and removing 

 the pineal body, the dorsal surface ot the thalamencephalon 

 will be sufficiently exposed to make out the following 

 features: 



(f) The slit-like aperture appearing in the middle line after the 

 removal of the pineal body represents the dorsal portion of 

 the third ventricle (ventriculus tertius) (Fig. 84), the roof 

 of which is formed anteriorly by the superficial portion of the 

 chorioid plexus (plexus chorioideus) , the latter entering the 

 ventricle at this point. 



(g) The lateral margins of the aperture are largely formed by two 

 minute spindle-shaped masses, one on either side, the 

 habenulae. Their posterior ends are united by a slender 



transverse band, the habenular commissure (com- 



missura habenularum). The fibres 

 ot the commissure are faintly 

 traceable forward, where they 

 form a pair of thin whitish fila- 

 ments (medullary striae), 

 (h) The posterior commissure 

 (commissura posterior) crosses 

 the posterior portion of the roof 

 immediately behind and below 

 the habenular commissure. 

 (i) The walls of the third ventricle 

 are formed by the thalami. 

 They are broadly connected by 

 the intermediate mass (massa 

 intermedia), or middle com- 

 missure, which may be seen 

 from the dorsal surface crossing 

 the cavity, 

 (j) On either side of the middle line, or of the habenulae, the 

 dorsal portion of the thalamus forms a low, somewhat oval 

 projection, the pulvinar or posterior tubercle." 



The anterior tubercle of the thalamus is a faint elevation of very 

 small dimensions lying in the angle enclosed between the pulvinar and 

 the anterior portion of the aperture of the third ventricle. 



Fig. 84. Diagram, showing the 

 arrangement of the parts of the 

 thalamencephalon as viewed from 

 the dorsal surface, after removal of 

 the pineal body: a., anterior 

 thalamic tubercle; c.h., habenular 

 commissure; c.p., posterior com- 

 missure; c.s., superior colliculus 

 (of mesencephalon); g.l. and g.m., 

 lateral and medial geniculate bodies; 

 h., habenula; m.i., massa inter- 

 media; p., pulvinar; v.t., third 

 ventricle. 



