314 



Class MAMMALIA. 

 Subclass IMPLACENTALIA. 



Order MONOTREMATA*. 



The principal osteological characters of this Order are : the second clavicle, or 

 ' coracoid,' extending, as in Birds and Lizards, from the scapula to the sternum, and 

 anchylosing at full growth with the scapula ; the epicoracoid, as in Lizards ; the 

 marsupial bones ; the supplementary tarsal bone supporting the perforated spur in 

 the male ; the long persistence of distinct pleurapophyses in the vertebra dentata. 

 All the species are pentadactyle on both fore and hind feet, and are devoid of true 

 calcified teeth. 



Genus Ornithorhynchus. 



1698. The partially disarticulated skeleton of a young Duck-mole, or Platypus (Or- 

 nithorhynchw paradoxus) . 



The cranium exhibits traces of many of its sutures, and some remain very evident, as the 

 coronal, fronto-nasal, and the suture between the exoccipitals and the superoccipital. The 

 auditory ossicles are preserved in situ. The horny teeth are displayed apart from the jaws. 

 The transverse processes of the atlas are perforated parallel to the anterior border of the 

 neural arch, from below upwards, forwards and inwards, for the passage of the vertebral 

 artery. The odontoid is not anchylosed to the axis ; it articulates with the neural arch, as 

 well as with the lower cortical portion of the body of the atlas, and it developes forward and 

 a little upward a long odontoid process. The true body of the axis bears neurapophyses and 

 a neural spine, upper and lower transverse processes and pleurapophyses, which last are not 

 anchylosed and leave a wide vertebral foramen, circumscribed by the articulation of the ' head ' 

 with the parapophysis, and of the ' tubercle ' with the diapophysis. The harmonise between 

 the diapophyses and pleurapophyses are obvious in the remaining cervical vertebrae, the arte- 

 rial foramen being completed by the anchylosis of the head of the pleurapophysis with the 



* Gr. ftovos, single, -j>//m/, hole : in reference to the single cloacal outlet for the excrements and 

 products of generation. 



