540 ME. JAMES JOHNSTONE OF THE 



surrounding tissues. They were about O'l millim. in length, 

 and of about the same width as the anterior lobes. There were 

 no connexions between anterior and posterior lobes. 

 I could find no trace of thymus-tissue in the neck. 



Thylacinus. A full-grown specimen : head-length about 21 

 eentim. 



The thymus (PL 37. fig. 4, tm.) lay partly in the neck, but 

 mostly in the thorax. It stretched down to about one-third 

 of the length of the heart from the base of the latter, 

 presenting at the posterior extremity a thin, flattened-out, 

 asymmetrical lobe. Some little distance above the first rib 

 it passed, without any decided transition, into an irregular 

 fat-mass (_/). It was very irregular in form, and showed in 

 its cervical portion a division into two lobes which were not 

 confluent posteriorly. It was most massive some little dis- 

 tance below the bifurcation of the carotids, and at this point 

 it covered the carotid fork and the origin of the right subclavian 

 artery. Altogether there were in the thymus a pericardiac 

 flattened-out portion ; a cervical extension ending about 4 eentim. 

 above the first rib, consisting of two paired, closely approxi- 

 mated lobes ; and an intermediate portion, elongated in a dorso- 

 ventral direction and somewhat irregular in form. The entire 

 organ, with the exception of the flat pericardial portion, seemed 

 to be compressed laterally in the narrow mediastinal space. 



On microscopic examination the ordinary structure of the 

 thymus was seen, except that everywhere the organ was invaded 

 by fat. Here and there the thymus-tissue was reduced to narrow 

 strands of cells ramifying among the fatty connective mass. 



The head of this specimen had been cut off", but on examina- 

 tion of it a number of glandular bodies could be seen lying 

 beneath the submaxillary glands. All of these were submitted 

 to microscopic examination, and proved to be ordinary lymph- 

 glands. There was no evidence of a detached cervical thymus. 



Myrmecdbius fasciatus. Foetus, 2 eentim. long. 



The thoracic thymus occupied the ordinary position, and was a 

 paired body, triangular in shape in longitudinal section. The 

 paired halves were not confluent. Marked secondary lobulation 

 had taken place, and the distinction in the lobules of cortical and 



