EPIPHYSIS CEREBRI 



581 



/.AC 



t. fee. ft. of 



7 C*,. 



of the stalk is limited basally by the habenular commissure, the posterior 

 wall by the posterior commissure. The pineal proper thus lies under- 

 neath the posterior end of the corpus callosum and rests on the anterior 

 pair of the corpora quadrigemina. It is a solid cone-shaped structure 

 enveloped by a cap- 

 sule of pia mater, and 

 more or less distinctly 

 lobed (Fig. 498). It 

 measures in man 7 

 mm. in length by 5 

 mm. in transverse 

 diameter. The mam- 

 malian pineal is per- 

 haps rather a meta- 

 morphosed than a ru- 

 dimentary organ. Its 

 size bears no relation 



to the size of the FlG 493. SEMIDIAGRAMMATIC REPRESENTATION OF A 



brain or the size of MEDIAN LONGITUDINAL SECTION THROUGH THE EPI- 



the body; it is no PHYSIS OF A 17 CM. SHEEP FETUS. 



larger in large than 



in small dogs, for example, and no larger in horse than in dog; that 



of sheep is about the size of that of man. 



Function. Injection of pineal extract of sheep into the blood of cer- 

 tain mammals produces only very slight effects. These, however, are fairly 

 uniform, but very transient. The most conspicuous effect is a slight fall 

 of blood pressure. There is also a slight improvement in the beat of the 

 isolated cat's heart, a transient diuretic effect (in rabbit) and a slight ir- 

 regular respiratory effect (in dog, cat and sheep Jordan and Eyster, Amer. 

 Jour. PhysioL, 1911). These results are, to some extent, the reverse of 

 those obtained with extracts of the hypophysis, and suggest a compensatory 

 or antagonistic regulatory functional relationship. Extirpation experi- 

 ments have not yet yielded perfectly satisfactory results. The evidence, 

 however, indicates a functional role which is negligible or nil. Clinical 

 evidence combined with autopsy findings indicate symptom complexes asso- 

 ciated with pineal tumors or other structural alterations in general like, 

 but of reverse relationship, to tnose present in case of hypophyseal altera- 

 tion; i.e., the symptoms of hypopinealism are in general those associated 

 with hyperpituitarism, and those of hyperpinealism like those accompany- 

 ing hypopituitarism. The symptoms associated with morbid conditions of 

 the pineal may possibly be the inherent result of pressure (or undue relaxa- 



