THE ANATOMY OF THE THYROID GLAND 155 



the branchial artery. Anteriorly it sometimes presents a narrow 

 process of gland-tissue running forward, and behind it is limited 

 by the bifurcation of the branchial artery." The contents of its 

 vesicles consisted of coarsely granular masses or globules of various 

 sizes which '' correspond with the 'colloid substance' of authors." 

 He surmises the non-existence of lymphatic vessels and says that 

 in both the skate and the conger-eel "an extensive system of 

 vessels lined with epithelium becomes injected by the method of 

 puncture" ; he considers that these are blood-vessels. The narrow 

 process of glandular tissue which Baber says is occasionally 

 present in Raia is more frequently seen in the Selachii; it is con- 

 stantly present in all the examples of Carcharias which I have 

 dissected. It extends forward until it comes into contact with 

 the anterior margin of the basi-hyal cartilage (lingual bone) which 

 presents a depression, frequently amounting to a complete fora- 

 men, for the reception of the anterior extremity of the glandular 

 process with the connective tissue by which it is heavily invested. 

 This process is obviously analogous to the pyramidal lobe of the 

 mammalian thyroid, and as it extends all the way to the pharyn- 

 geal submucosa in many instances it may well be considered as 

 indicative of a phylogenetic connection of the gland with the cavity 

 of the pharynx, a condition which is also indicated by the on- 

 togeny of the organ in all the orders, and which appears to be 

 permanent in the Ascidians, Amphioxus, and the Cyclostomes. 



Baber's suspicion of the non-existence of lymphatics within 

 the thyroid gland appeared to the writer to be such a remarkable 

 observation and so out of harmony with the known anatomy and 

 physiology of the organ in the higher animal orders as to require 

 further study. This study was pursued by means of a consider- 

 able series of careful dissections with many injection experiments 

 and did not appear to confirm Baber's opinion. Baber's obser- 

 vation that the blood-vessels in these animals could be injected 

 by the method of puncture is quite accurate, but it does not by 

 any means disprove the existence of lymphatics. His results were 

 apparently dependent upon the fact that the smallest veins and 

 capillaries are of very considerable caliber and readily admit of 

 injection, while the lymphatics are very minute and are entered 



