THE ANTERIOR LOBE OF THE PITUITARY BODY. 1809 



Wall of diencephalon 



Posterior (cerebral) lobe 



thus represents the condition existing in some animals, in which the pituitary stalk 

 persists during life, passing through a canal in the base of the skull and connecting 

 with the oral epithelium. During the latter half of the second month the hypophys- 

 ial sac sends tubular outgrowths 



into the surrounding vascular meso- FIG. 1534- 



blastic tissue. Later these tubules 

 become separated from the main 

 pouch, which latter often persists 

 and becomes surrounded by acini 

 to form the pars intermedia. The 

 tubular outgrowths of other parts 

 of the anterior lobe lose, in large 

 part, their lumina and become 

 solid cords separated by capillaries. 

 The anterior lobe thus formed be- 

 comes pressed against the under ",';" -l^^g 

 surface of the brain-lobe with ; ':^a^ 

 which it is closely bound. ''&"'( 



The posterior pituitary lobe 

 is developed from the tubular ..v'^vl 

 outgrowth from the diencephalon 

 and retains its connection with the 

 brain through the infundibulum. 

 The primary lumen, however, be- Ji 

 comes obliterated and the organ 

 converted into a solid mass com- 

 posed of tissue which resembles 

 neuroglia and contains few or no 

 cells that can be identified as ner- 

 vous elements. Further details concerning the posterior lobe are given in connection 

 with the brain (page 1130). 



Cartilage of 

 base of skull 



.Wall of oral cavity 



Portion of sagittal section of rabbit embryo, showing later 

 stage of developing pituitary body. Anterior lobe now con- 

 sists of numerous tubular acini. X 50. 



As a matter of convenience, mention may be made at this place of three organs 

 the carotid bodies, the coccygeal body and the temporary aortic bodies concerning 

 whose function little or nothing is known. The systematic position of these struc- 

 tures is at present uncertain, but from their histological characteristics the carotid 

 and aortic bodies are probably to be regarded as closely related to or, in a sense, 

 appendages of the system of sympathetic nerves, whilst the coccygeal body may be 

 included, with seeming propriety, with the organs of internal secretion. Their 

 grouping and description here, therefore, must be understood to be a matter of con- 

 venience and expediency and not an attempt to define their true relations. 



THE CAROTID BODY. 



This organ (glomus caroticum), also known as the carotid gland and ganglion 

 intercaroticum, is a small ovoid body measuring usually about 5 mm. in length, from 

 2.5-4 mm - m width and about 1.5 mm. in thickness. It may attain a length of 7 mm. 

 and exists on both sides. Its most frequent position is on the median and deep side 

 of the upper end of the common carotid artery in close relation with the point of 

 division of the latter vessel into the external and internal carotids. The body 

 usually lies not within the bifurcation, but rather on the inner side of the common 

 carotid, so that its form and relations are best displayed by dissection from within 

 outward. When freed from the surrounding fat and connective tissue, the carotid 

 body appears of a grayish or brownish red, according to the condition of the capillary 

 injection. The organ consists sometimes of two unequal divisions, united below. 



Its structure includes a thin fibrous capsule, from which delicate septa pene- 

 trate inward and divide the organ into a small and uncertain number (5-15) of 

 spherical masses or "lobules," from .2-. 5 mm. in diameter, which consist of a com- 



114 



