24 



On the Anatomy of the Thyroid Body in Man. [June 20^ 



that the cross sections of any two muscles tending to produce a similar 

 effect are directly proportional to tlie cross sections oftlieir tendons. 



I shall select as an example the case of the flexor liallucis longus and 

 flexor digitorum communis perforans of the Ehea, whose tendons unite 

 into a common tendon halfway down the posterior side of the canneon 

 bone of the bird. 



The cross sections of these two muscles are shown in the annexed 

 figures, taken as in the human subject. (Figs. 7 and 8.) 



The areas of these cross sections were found to be as 245 to 160 ; or 

 the lesser was 65 per cent, of the greater. 



Two equal lengths of the dried tendons were then weighed and found 

 to be in the proportion of 845 to 495, which was assumed to be the 

 proportion of their cross sections. The lesser of these numbers is 

 59 per cent, of the greater ; a result that seems to be as near to the 

 former result derived from the muscles, as can be expected in this class 

 of experiments. 



IV. Observations on the Anatomy of tbe Thyroid Body in Man.^' 

 By George W. Callender^ Lecturer on Anatomy at St. 

 Bartholomew's Hospital. Commujiicated by Mr. Paget, Re- 

 ceived June 8, 1867. 



(Abstract.) 



Much doubt exists as to the earliest connexions of the thyroid body, 

 whether it is developed, that is to say, with the membranous air-tube, 

 or has a common origin with the thymus gland. There are no re- 

 liable observations as to the formation of the isthmus or as to the origin 

 of the pyramid, so far, at least, as man is concerned, although, with 

 reference to the isthmus, its absence in an entire class, that of birds , 

 and the observations of Grray on the formation of the thyroid in the 

 chick, countenance the supposition that it results from the growing 

 together of two lateral masses. 



In a human foetus, between the seventh and eighth week, the thyroid 

 body is closely connected with]|the trachea and with the lower edge of the 

 larynx, and although consisting of but one piece is deeply notched, and 

 thus looks as though made up of three separate lobes. It is quite 

 distinct from the thymus, as may be further seen in the dissection of 

 a foetal rabbit or foetal pig, in which, whilst firmly attached to the 

 trachea, it has no kind of connexion with the thymus. In the human 

 foetus no distinct evidence of the thyroid appears to exist before the 

 sixth week, up to which time it cannot, I believe, be isolated from the 

 structures in front of the neck. It seems to come out from the blastema 

 in the form of a mass in front of the trachea, and quickly acquires an 

 imperfectly lobed appearance. 



In the dissections referred to, the presence of a middle portion and its 



