758 BR R. BJtOOM ON 



ridge and commencing ectostoses radiating from its margins over a small part of the surface 

 of the cartilaginous scapula, both the scapula and coracoid are entirely cartilaginous. 



The coracoid has a very peculiar structure. It consists of an upper and a lower 

 part, with a connecting neck. The upper part presumably forms the anterior third of 

 the glenoid cavity. In both Trichosurus and Pseudochirus the coracoid part of the 

 glenoid cavity is formed by an excavation of the coracoid cartilage, but here, in addition 

 to tke simple excavation, the cavity is enlarged by a well-developed outstanding rim 

 w T hich projects downwards from the coracoid and forms the inner margin of the margin, 

 somewhat after the style of the well-marked rim in Ornithorhynchus. From the 

 glenoid cavity the coracoid passes almost directly inwards for a short distance, and the]) 

 passes downwards and slightly backwards as a comparatively narrow neck, which is 

 continued into the large inferior part of the coracoid. A very deep groove is formed 

 between the coracoid rim of the glenoid cavity and the descending neck, and to the 

 anterior part of this groove is attached the long head of the biceps. The inferior part 

 of the coracoid is a long, broad, flattened structure which passes from the lower end of 

 the neck backwards and slightly outwards. Near its middle it adjoins the sternum, and 

 is structurally continuous with it. Posteriorly it rests on the first rib, but is distinct 

 from it. 



The clavicle is unusually flat. In its outer third it is slender and rounded, but in 

 its inner two-thirds it is almost quite flat. From the anterior rounded portion a ridge is 

 continued for a short distance along the outer border. The posterior end passes between 

 the coracoid and the sternum, and rests on the upper side of the sternum. Round i h> 

 whole outer third of the clavicle is a thick coating of large cells, the more central of 

 which are cartilaginous. A similar coating is found round the inner end, and here again 

 many of the cells are cartilaginous. 



I fail to detect any trace of an omo-sternum. 



The Morphology op the Scapular Borders. 



In all marsupials, and practically all the higher mammals, the scapula is formed on one 

 and the same plan, and all the variations met with are due to different degrees of 

 development of the different regions. According to Flower (5), " the scapula may be 

 considered as essentially an elongated rod or bar of bone," which usually has "three 

 projecting plates or ridges arranged round the longitudinal axis, and three surfaces or 

 fossae bounded by these." This is also the view taken by Parker (4), who has given the 

 following special names to the projecting plates : — The prsescapula, mesoscapula, and 

 postscapula. While such a manner of looking at the scapula is very convenient for the 

 hio;her forms, it leads to confusion when the lower forms are considered. In almost all 

 reptiles, the scapula, instead of being made up of an anterior, a posterior, and a median 

 plate, has but two borders, an anterior and a posterior, and even in the monotremes 



