76 ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. 



phalo-mesenteric arteries, do not become converted into organs 

 of special structure, but retain during life the original consti- 

 tution of the menibrana intermedia of the blastoderma, and 

 increase rapidly in the embryo, constituting the supra-renal 

 capsules. Whatever doubt may be entertained as to the exact 

 functional import of these bodies, the identity of their ana- 

 tomical constitution with that of the blastoderma is sufQciently 

 evident, and their morphological signification appears to be 

 equally so. 



That portion of the membrana intermedia ^Yhich is situated 

 between those two aortic arches, the extremities of which 

 become the carotid and subclavian arteries, remains during 

 life as the thyroid body. It receives its blood from the first 

 and second aortic arches by two large trunks on each side, the 

 superior and inferior thyroid arteries. 



That portion of the membrane which passes in two parts 

 from near the base of the cranium back as far as the ductus 

 Cuvieri and anterior portions of the veins of Eathke, and 

 which are united and concentrated in front of the heaii by 

 passing from behind forwards, in harmony with corresponding 

 motions of the neighbouring part, becomes the th}Tnus. 



The structure of these three organs is identical with that 

 of the blastoderma. Their probable function — namely, to 

 prepare by the action of their nucleated cells, and to throw 

 into the vascular system, a matter necessary for the nutrition 

 of the animal during the period of its active growth — a func- 

 tion which the observations and opinions of the majority of 

 physiologists have assigned to them — is also essentially the 

 same with that of the blastoderma. 



The question as to the exact or intimate nature of the 

 function of these organs can only be answered by further in- 

 quiries in chemical physiology. It appears to me to be suffi- 

 cient at present to insist that their fimction, as deduced 

 from their structure and anatomical relations, is similar to 



