ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



degenera'e and membranous, with a choroid plexus of blood-vessels 



,sed to it. Its cavity, the ."third ventricle/' is a narrow 



! slit, on each side of which is a thick lateral wall known as 



the optic thalamus and composed for the most part of sensory nerve- 



iibres on their \viiy from the eye towards the optic lobe. 



From the posterior portion of 

 the roof of the thalamencephalon 

 there projects a slender tubular 

 outgrowth which stretches for- 

 wards and ends blindly close to the 

 skin of the dorsal surface a little in 

 front of the hemisphere region. 



mo. 



Xlat 



X.v. 



IX 



FIG. 138. 



I'.r.tin of Ai-anthias with the cranial nerves (after Purser), c, Cerebellum ; h, hemisphere region ; 



km, hyomandibular brain h of VII ; i.l, inferior lobe ; m.o, medulla oblongata ; o.l, olfactory bulb ; 



thahnk branch of V; op.l, optic lobe; pit, pituitary body; th, thalamencephalon. 



II. ' [II, ' nlomotor ; IV, pathetic; V, trigeminal, V.o, its superficial ophthalmic 



.; VI, abducent; VII, facial, VIIo, its superficial ophthalmic branch; VIII, auditory; 



'.'h.irynKral ; X, vaults l>j , 1)2, etc., its branchial branches, \.ldt. its lateral line 



r..l branch. 



This U the pineal organ of great interest from the fact that in most 



[unctions as a ductless gland while in a few members of 



p it takes the form of a third eye. It will be referred to in 



xion latrr on. 



tloor of the thalamencephalon dips downwards into a large 



ing pocket the infundibulum. The side-walls of this 



to form the inferior lobes (Fig. 138, B, i.l) while its terminal 



