THTMrS IK THE MAESTJPIALS. 543 



the origin of tlie great vessels. This mass of tissue was some- 

 what irregular in shape, and was asymmetrical, lying almost 

 entirely to the left side. I searched for traces of a cervical 

 portion, but was not able to recognize any such structure. 

 Various bodies in the neck having the appearance of adenoid 

 tissue were examined microscopically, but proved to be nothing 

 more than small lymph-glands. The mass lying on the origin 

 of the great vessels was found to be a true thymus. 



(In this specimen the innominate artery branched, after 

 springing from the aortic arch, into the left subclavian and a 

 common trunk, which gave origin to the right and left carotids. 

 The right subclavian artery was given oif from the right carotid 

 jast above the origin of the latter from the common trunk.) 



V. Macropodid^. 



I have not examined any adult forms belonging to this 

 family, but I have sectionized a foetus Macropus JLugenii about 

 21 millim. in length, and of Macropus Wilcoxii of about the 

 same length. I have also examined sections cut from a foetal 

 Macropus belonging to Mr. M. F. Woodward, the species of which 

 I am unable to determine. 



In M. ISugenii the thyroid was represented by a median 

 unpaired, and by lateral paired parts. The thymus consisted of 

 cervical and thoracic portions, which had no connexion with each 

 other. The thoracic portion consisted of two separate portions 

 on each side which lay longitudinally. The cephalic lobes 

 differed notably from the caudal lobes in histological structure. 



The Thyroid. 



The lateral paired lobes of the thyroid were in their greatest 

 length about 0'45 millim. They were somewhat rounded 

 masses, but rather elongated internally, and lay posterior to 

 the cricoid cartilage of the larynx. In this specimen the long 

 axis of the head formed a right angle with the longitudinal 

 axis of the body, so that the submaxillary gland lay at about the 

 same transverse level as the atlas vertebra. The lateral thyroids 

 lay in this plane, almost touching the submaxillary glands. 



The median thyroid lay in the same plane as the lateral lobes, 

 wedged in between the sternothyroid muscles and the trachea. 

 It was only approximately median and unpaired. In its greatest 



