150 THE VOYAGE OF H.M.S. CHALLENGER. 



observed by Professor Turner to proceed from the superior maxillary division of the fifth ; ' 

 again, every demonstrator of anatomy has observed the descendens noni taking its origin 

 from the vagus instead of the ninth nerve ; and the frequency of the accessory obturator 

 and the accessory phrenic nerves is a fact of common knowledge. The Cetacea afford 

 us a very striking illustration. The absence of functional hind-limbs and the massing of 

 the muscles in the posterior part of the animal into four great columns, which are situated 

 one upon each aspect of the spine, give rise to a corresponding adaptation of the nerves. 

 Thus we find that the lumbo-caudal nerves, after giving off branches to the genitals and 

 the abdominal wall, arrange themselves in four nerve-cords, which extend backwards 

 upon the vertebrae to the tail. Each cord is developed in relation to one of the four 

 fleshy columns. 2 The arrangement is peculiar to the Cetacea, and probably also the 

 Sirenia. 



Thoracic Viscera. 



The thoracic viscera were examined in each specimen that was put into my hands, 

 viz., in the Thylacine, the Dasyure (Dasyurus viverrinus), Cuscus, Vulpine phalanger 

 and Phascogale. I now propose giving a sketch of the peculiarities which were noted. 



Pericardium. 



In Thylacinus the pericardium is oval or fusiform in shape — considerably narrower 

 behind than in front. Posteriorly the fibrous layer presents a slight attachment to 

 the diaphragm, whilst anteriorly it is lost upon the coats of the aorta and great 

 vessels. Two indefinite fibrous bands, the sterno-pericardiac ligaments, bind its lower 

 surface to the upper aspect of the sternum. In addition to the usual vessels the 

 fibrous pericardium is pierced, in front of the root of the left lung, by the left superior 

 vena cava. The serous pericardium reaches the surface of the heart in the usual manner. 

 There is, however, no trace of the vestigial fold of Marshall. 



In the Dasyure, Phalanger, and the Phascogale, the fibrous pericardium presents 

 no direct attachment to the anterior surface of the diaphragm. In Cuscus, however, 

 a distinct fibrous band passed between these structures. This was not observed in the other 

 animals. In other respects the pericardium of each agrees with that of the Thylacine. 



Heart. 



Owen considers the Marsupial heart to be distinguished by three leading peculi- 

 arities, viz., (l) a bifurcation of the appendix of the right auricle into two angular 

 processes which embrace the root of the aorta ; (2) the absence of the annulus and 

 fossa ovalis — a condition which doubtless points to the short intra-uterine life of the 

 foetus, and (3) the absence of the terminal aperture, in the right auricle, of the " coronary 



1 Journal of Anat. and Phys., vol. i. ; and Proc. Royal Soe. London, 1868. 



2 Vide Cunningham, Spinal Nervous System of Porpoise and Dolphin, Journal of Anatomy and Physiology, vol. xi. 



