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54 PROF. OWEN ON THE ANATOMY OF THE INDIAN RHINOCEROS. 



The relative longitudinal extent of the great commissure or ' corpus callosum ' is 

 shown at s, s, in the view of the vertical section of the brain of the female Rhinoceros 

 given in PI. XXII. fig. 1. A septum lucidum, 5, of moderate extent, connects the under 

 surface of the anterior half of the corpus callosum with the fornix : in the same section 

 the optic thalami are seen at ; the ' plexus choroides ' at p ; and the mass of the 

 quadrigeminal bodies at k. The arrangement of the grey and white matter in the lobes 

 and lobules of the cerebellum, forming the ' arbor vitEe,' a, is also shown: this is less 

 complex than in the Horse. 



The lateral ventricle is laid open by the removal of its outer wall to show the size 

 and shape of the great hippocampus at 7i, fig. 2, PI. XXII. ; and in the same figure are 

 shown the ' plexus choroides ' p, passing through the ' foramen Monroianuin ' m, beneath 

 the crura of the fornix and the outer lamina of the septum lucidum, q. The left lateral 

 ventricle is laid open from above to show the proportions of the ' corpus striatum '/, 

 with the hippocampus i, and the intervening part of the fornix, covering the optic tha- 

 lamus h, together with the ' plexus choroides ' p. In PI. XXI. the corpus callosum s, s, 

 has been bisected and the hemispheres divaricated to show the forms and proportions 

 of the bigeminal bodies ; of which the posterior pair b are broader but shorter than 

 the anterior ones a. The pineal gland is shown at n ; the optic thalamus at h ; the 

 ' plexus choroides ' at p ; and the ' corpus striatum ' at/. 



The commencing decomposition of the inner substance of the brain prevented the 

 better definition of some of the other parts of this organ. 



The common anastomotic trunk of the basilar or vertebral arteries, after traversing 

 the median line of the pons, gives off a pair of arteries at right angles, which cross the 

 crura cerebri between the pons and the third pair of nerves : a second pair of transverse 

 branches is sent off just anterior to the former, and receive the anastomosing longitu- 

 dinal branches from the ento-carotids which complete the circle of Willis. From the 

 ento-carotid parts of the circle, a branch is given off to the interspace between the 

 middle and anterior lobes of the cerebrum, where it divides into three or four branches. 



The eyeballs are of small comparative size ; each measured in antero-posterior 

 diameter one inch five lines, and in transverse diameter one inch three lines. Some 

 dark-brown pigment lies under the conjunctiva for the extent of about a hne from the 

 circumference of the cornea : the same kind of pigment is also deposited upon the 

 outside of the nictitating eyelid, and over a great part of the inner surface of the same 

 part, covered of course by a reflection of the conjunctiva. The trunks of the venae 

 vorticosBE perforate the sclerotica half-way between the entry of the optic nerve and 

 the edge of the cornea. I injected one of these veins with mercury, which immediately 

 returned by vessels perforating the sclerotica near the optic nerve. The disposition of 

 the vense vorticosee, with the flocculent but somewhat firm connecting tissue of their 

 radiating branches, presented that structure which most nearly resembled the figures 

 given by Mr. Thomas of the parts he describes as "processes having a muscular 



