568 DR. C, F. SONNTAGt ON THE COMPARATIVE ANATOMY 



beyond the posterior edge of the right lobe when fully distended 

 with bile. 



The Ductless Glands. 



Phascolarctos cinereus. 



The Thyroid Gland (text-fig. 56, A, A). — The two lateral lobes 

 are vinconnected, and vary in shape and extent. The left lobe is 

 pja-iform, with the broad extremity posterior and slightly within 

 the thorax. It is 2 cm. long, "8 cm. wide, and '3 cm. thick. It 

 is sepai-ated from the larynx by the first three tracheal 

 rings. The right lobe is elongated and ovoid, and measures 

 2-7 X '5 X "S cm. Its anterior extremity overlaps the lower end 

 of the larynx, and its posterior pole stops anterior to the thorax. 

 The artericd sufply comes from the thyroid and laryngeal branches 

 of the common carotid artery (7?i), and the vehts run to the 

 internal jugular vein (li). 



I did not observe any structures which could be definitel}' 

 described as 'parathyroid bodies, but they may have been lying 

 among the small glands which are numerous at the root of the 

 neck. 



The Thymus Gland has been described by Symington (15). 



The Sup7-arenal Cajysides (text-fig. 61, s.R.c). — The left capsule 

 is a round body, of the size of a large pea, lying on the mesial 

 aspect of the anterior pole of the left kidney, to which it is 

 attached by a fold of peritoneum. The right capsule is oval, and 

 has a peculiar position ; it lies in contact with the posterior 

 surface of the liver, and is situated between the inferior vena 

 cava to the right, the right crus of the diaphragm to the left, 

 and the oesophagus ventrally. 



The greater part of each capsule is composed of brown 

 medulla. 



The spleen has been described by Martin (8). 



My specimen is triangular and measures 7 '4 cm. long, but 

 that of Trichosurus mdpecula has a lateral process (text-fig. 61, 

 F and G). In Phascolomys it is an equilateral triangle. 



Trichosurus vulp)ecida. 



The lateral thyroid lobes (text-fig. 57 A) measure 1"3 cm. long 

 and 'S cm. wide. They lie at the sides of the posterior extremity 

 of the larynx and antei'ior seven tracheal rings. The connecting 

 isthmus crosses rings 5, 6, and 7. 



The thyroid artery describes a curve, with the convexity 

 forwards, and runs along the anterior five-sixths of the m.esial 

 border of its corresponding lateral lobe. The thyroid vein runs 

 to the internal jugular vein (jo). This arrangement of the thyroid 

 vessels is seen in animals belonging to several of the Mammalian 

 orders. 



