866 DR. C. p. SONNTAG ON THE VISCERAL ANATOMY 



The Heart : — In all Marsupials the apex is formed by the left 

 ventricle, and the right ventricle falls short of it by a variable 

 interval. Cunningham (3) stiites that the right venti'icle in 

 Thylacinus stops short of the apex by 1| inches, but I never 

 observed such a long interval in any Marsupial. In very young- 

 pouch specimens the right ventricle is relatively longer than in 

 adults. 



Owen (11) describes bifurcation of the right auricular appendix 

 as one of the chief characteristics of the Marsupial heart, but 

 some species have no trace of a division, and in others the division 

 has no reference to the ascending aorta. 



The appendix is conical and bifid in Petaurus sciureus and 

 pouch specimens of Macropus hennetti and Macropus gigantetis, 

 but the two divisions are small. In Dendrolagus iirsinus and 

 Perameles ohesula it is large and round ; and the former has a 

 well-marked process lying on the dorsal aspect of the aorta, but 

 no trace is present in the latter. Cunningham pointed out that 

 there is no bifurcation in Thylacinus and Dasyurus, but there is 

 a strong division in Cuscus and Trichosurus. A slight division is 

 present in Phascogale, but it has no reference to the ascending 

 aorta (3). In Phascolarctos cinereas the secondary process is large, 

 and the right precaval vein passes into it. 



The characters of the interior of the auricles and ventricles 

 of many Polyprotodonts and Diprotodonts have already been 

 described by Cunningham. 



The Aortic Arch : — In all Marsupials it describes a full curve 

 and ends at the level of the fourth dorsal vertebra, and the 

 relations are similar in all forms to those described in the Koala 

 (15). The branches differ considerably, for six types are present, 

 as shown in text-fig. 76 C-F. 



1. Both carotids and subclavians arise separately, so no inno- 

 minate artery is present — Phascolarctos civ.ereus f. 



2. The two subclavian and the innominate arteries are given 

 oflF, and the latter divides into the two common carotid arteries — r 

 Dasyurihs macrurus (C). 



3. The branches arise as in Man — Phascolarctos cinereits*, 

 Petaurus breviceps*, and Phascoloimys mitchelli (D). 



4. The innominate artery gives off the left common carotid 

 artery, and divides into the right subclavian and right common 

 caxotid arteries — Trichosurus vulpecula'f. 



0. The innominate artery gives ofi the right subclavian artery, 

 and is continued as the bicarotid trunk which divides into the 

 two common carotid arteries — Thylacinus harrisi, Diclelphys can- 

 crivora, Dasyitrus viverrinus, and Petaurus ausiralis * (E). 



6. The innominate artery gives off the right subclavian and 

 both common carotid arteries at the same level — Citscus onacu- 

 latus, Dendrolagus ursinus, Phascolarctos cinereus *, and Macvopus 

 gigaitteus (F). 



* These observations are recorded in bitlierto unpublished notes by Garrod. 

 t These tj'pes have been figured in my paper on the Koala. 



