EP1PHYS1S CEREBEI 



581 



. Sec. ft. of 



"" 



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 eallosum 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 



lubed (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 495. SEMIDIAGRAMMATIC REPRESENTATION OF A 



MEDIAN LONGITUDINAL SECTION THROUGH THE EPI- 



PHYSIS OF A 17 CM - SHEEP FETUS ' 



sze 



brain or the size of 

 the body ; it is no 



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 rule 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 those present in case of hypophyseal altera- 

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

 with hyperpituitarism, and those of byperpinealism 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- 



