134 ANATOMY OF THE RABBIT 



still problematical, but an extract has been shown to increase 

 fertility and when administered through successive generations to 

 produce accruing precocity- in development. The gland becomes 

 lymphoid in character at some time after birth and is more or less 

 reduced after the animal reaches maturity. There is some evidence 

 which has been interpreted as indicating antitoxic activity. 



The Hypophysis 

 The hypophysis is embryonically of double origin, while structur- 

 ally three major divisions are recognized, viz: lobus glandularis, 

 lobus nervosus, and infundibulum. The first of these comprises a 

 pars distalis, a pars tuberalis, and a pars intermedia (Fig. 80), and 

 the infundibulum is subdivided into the median eminence of the 

 tuber cinereum and the infundibular stem. The glandular lobe is 

 derived from the epithelium of the roof of the mouth, while the 

 remaining parts are an outgrowth from the brain. Experimental 

 removal of the pars distalis retards growth in young animals, the 

 body retaining an infantile condition, and in normal circumstances 

 the growth hormone produced is concerned in protein metabolism. 

 Hyperactivity of this part in human adults is associated with the 

 condition known as acromegaly, abnormal enlargement of the 

 hands, feet, or parts of the head. The pars distalis also secretes 

 hormones concerned in ovulation, in lactation, and in the stimu- 

 lation of other endocrines. The neural lobe (lobus nervosus) pro- 

 duces a substance similar in some respects in its action to adrenalin 

 and, like the latter, related functionally with the activity of the 

 sympathetic system. It restricts cardiac output and oxygen con- 

 sumption. Possibly, one component regulates passage of sub- 

 stances through the walls of capillaries, and another may stimulate 

 uterine contractions in parturition. 



The Pineal Gland 



The pineal body is also an unpaired outgrowth of the brain, 

 being the product of a part which in lower vertebrates displays the 

 potentiality of developing into either a sense organ (a light-receptor) 

 or a gland. In mammals it is always an endocrine gland. Its 

 functions are not yet well understood but it has been reported to 

 produce a growth-regulating substance, or one accelerating 

 differentiation. 



