544 MR. JAMES JOHNSTONE ON THE 



length it was about 0'15 millim., and ia transverse diameter it 

 measured 0"39 millim., so that it was elongated transversely. 

 There was no evidence of a median constriction, and there was a 

 delicate prolongation on its anterior border. In histological 

 character it consisted of short tortuous strings of cells staining 

 less intensely with carmine than those composing the thymus. 

 As a rule these cellular cords contained no lumen, but here 

 and there was a denser aggregation of cells at their periphery. 

 Anastomoses were not frequent. The median lobe lay in a 

 sort of cavity, across which septa of connective tissue passed 

 into the interior of the body, running between the cellular 

 springs. 



In tliis specimen of M. JEugenii there was no connexion between 

 median unpaired and lateral paired lobes. In another series of 

 sections I made of a foetus oiM. Wilcoxii of about the same length, 

 I found no median lobe existing, but only the lateral lobes, 

 connected by an incomplete bridge of thyroid tissue passing round 

 the trachea from the lower borders of the lateral portions. 



There was no trace of a foramen caecum or a thyroglossal duet. 



The Thoracic Thymus. (PI. 38. fig. 6.) 



The thoracic portion of the thymus in M. Eugenii consisted of 

 a paired series of parts. It lay almost in the median line of the 

 thorax, in the loose connective tissue in the interspace between 

 sternothyroid muscles (m.st.), trachea, and oesophagus («?), and 

 about halfway between the top of the sternum (st.) and the anterior 

 limit of the pericardium (p), and some little distance above the 

 origin of the sternothyroid and sternohyoid muscles. It was very 

 small, only about 0"5 millim. in its greatest length; the paired parts 

 were not in actual contact, but were separated by an interval of 

 about O'l millim. Each half consisted of two lobes, which may 

 be called anterior (tm.a.) and posterior (tm.p.), since they lay 

 in the longitudinal line of the body. They were approximately 

 equal in size. The two vagi passed along their dorsal surfaces. 



These two lobes differed very notably in histological structure. 

 The inferior one {tm.p.) presented all the appearance of a 

 thymus ; that is, it was composed of small closely compressed cells, 

 which gave a deep coloration with borax-carmine. There was 

 no distinct capsule, and the mass seemed simply to lie embedded 

 in the ordinary connective tissue of the region. A narrow 



