THE ISTHMUS. 681 



peduncles of the conarium (or hahence). These (Fig. 323, 15) are two 

 narrow white bands, which commence at the base of the pineal gland, and 

 are directed forward parallel to each other, in the bottom of the fissure of 

 the thalami optici, to which they firmly adhere. On arriving at the anterior 

 common opening, they become attached to the anterior pillars of the cerebral 

 trigonal (or crura of the fornix). Sometimes they are very narrow and 

 separated by an interval ; but more frequently they are relatively wide, 

 and immediately in contact on the median line. 



The conarium is far from always offering the same volume ; it has 

 been exhibited in its usual dimensions in Figure 323, and in Figure 327 

 it is shown as incomparably larger. 



The structure of the pineal gland appears to be very simple, and only 

 comprises one substance of a brownish-grey colour, apparently amorphous, 

 and sometimes studded with calcareous granulations (acenulus), but with- 

 out any internal cavities. 



This organ and that whose description follows, do not belong, properly 

 speaking, to the system of the encephalic isthmus ; but are rather, as we 

 have already said, appended glands, which merit to be described apart, the 

 same as the three immense cerebellar and cerebral ganglia. If we have 

 studied them in this place, it was only for the sake of simplification. 



9. Pituitary Gland. (Figs. 322, 8 ; 327, 19.) 



The pituitary gland, also named the hypophysis cerebri and suprasphe- 

 noidal appendage, is a small disc-shaped tubercle, fixed to the anterior 

 extremity of the interpeduncular fissure by the pituitary stem (infundihdum) 

 and the tuber cinereum. 



a. The tuber cinereum is a little eminence of a grey colour, situated in 

 the middle line, between the corpus albicans and the chiasma of the 

 optic nerves, at the anterior limit of the encephalic isthmus. This emi- 

 nence is hollow, and its cavity is nothing more than a diverticulum of the 

 middle ventricle. 



h. The infundibulum is only a short conical prolongation, whose base is . 

 attached to the tuber cinereum, and its apex to the superior face of the 

 pituitary gland. The cavity of the tuber cinereum is continued into the 

 infundibulum, and terminates in. a cul-de-sac towards its summit. This 

 prolongation, also formed of grey substance, is distinguished by its great 

 fragility ; so that it requires some care to preserve it intact when opening 

 the cranium at its base. . . 



c. The pituitary gland is lodged in the sella turcica, where it is en- 

 veloped by the suprasphenoidal duplicature of dura mater ; it is a small, 

 nearly circular body, flattened above and below, and more or less thick, 

 according to the subjects. 



Its inferior face rests on the sphenoid bone through the medium ot the 

 dura mater, to which it is strongly adherent ; the superim- covers the corpus 

 albicans, with a portion of the cerebral peduncles, and m front receives 

 the insertion of the pituitary stem. Its circumference responds to the supra- 

 sphenoidal duplicature, whose interior forms the cavernous smus. 



There is no cavity in the pituitary gland. The matter composing it 

 appears to be almost amorphous ; it is yellow in the anterior half of the 

 organ, and brown in its posterior portion. 



