226 Basic Structure of Vertebrates 



Fig. 192. Left lateral view (seen as a transparent object) of the head and 

 heart of 50-hour chick embryo. (After Prentiss. Courtesy, Patten: "Early Embry- 

 ology of the Chick," Philadelphia, The Blakiston Company.) 



vertebrate groups justifies the assumption that the gland has an 

 endocrinal function throughout the series. 



Functions. One of the important functions of the anterior lobe is 

 stimulation of growth. Enlarged pituitary in early life is accompanied 

 by excessive growth of bone. Deficient secretion, on the other hand, 

 produces a certain type of dwarf, the ateliotic dwarf or "midget." 



After the growth of the long bones has ceased, as in the normal 

 adult, it is of course impossible to stimulate further growth in height. 

 But when, as the result of tumorous enlargement, anterior-lobe secre- 

 tion is increased, a local growth of bone, sometimes asymmetric, may 

 occur. Such cases of acromegaly are not infrequent. Experiments 

 demonstrate that deficiency of anterior-lobe hormone in young animals 

 results in failure of sexual development and atrophy of the sex glands. 



Of all the endocrinal organs, the pituitary is most important in 

 that it produces not merely one but numerous hormones, some of 

 which act directly on various parts of the body and others affect 

 the activities of other endocrinal organs, especially the adrenals 

 and the thyroid. Therefore, either directly, or indirectly through these 

 interrelations with other glands, the effects of the pituitary probably 

 extend to every part and function of the body. Hormones of the 

 anterior lobe, in addition to their control of growth, are essential to 

 the normal development and functional activity of the reproductive 

 organs, including the mammary glands. They affect processes so unlike 

 as the deposition of fat and the movements of pigment-granules in 

 black pigment cells (melanophores) of amphibian skin. The functions 

 of the posterior lobe are apparently less important — at least, less 

 numerous or less well known. There is evidence that it exercises some 

 control over metabolism, especially with reference to water, fats, and 



