8â J. ÊEARÎ), 



dition seen in the preceding embryo. The eyes and external ears are, 

 as in the younger example, completely covered by the thick epi- 

 trichium. 



The foetus was treated in the same way as the uterine form. 



In section. There are now tooth-germs on the dental ridge, 

 but no evidences as yet of enamel or dentine. The tongue is concave 

 above in section, strong, and possesses well-developed muscles. Saliv- 

 ary glands are present. Jacobson's organ is fully formed, the choana 

 is open and the olfactory organ in an advanced state of development. 

 The lachrymal duct is hollow, and opens below into the nasal chamber. 



There are hair-follicles, especially on the snout and the cheeks, 

 under the epitrichium. 



The eye. The retina is about half pigmented. Lens-fibres are 

 in formation, but there is a considerable cavity in the lens. There 

 are no rods and cones in the retina. The eye-lids are closed. 



The external ear and meatus are formed, but both are covered by 

 the epitrichium, which also fills the latter. The semicircular canals 

 are complete, and the ear of the mammalian type. 



There is as yet no ossification in the lower jaw. The hypo- 

 physis cerebri exhibits marked budding. 



The trachea has well-developed cartilaginous rings. The thymus 

 is fully formed. Largely ossified clavicles and a cartilaginous sternum 

 are present, in addition to cartilaginous ribs. 



The notochord is markedly constricted in the cervical and thoracic 

 regions. The latter region greatly exceeds the abdomen in dimensions. 



The entire skeleton of the fore-limb is cartilaginous, and there 

 are powerful claws on the digits of the hand. 



The red blood-corpuscles are still (apparently all) nucleated ^). 

 In the heart the foramen ovale is quite closed. The lungs are highly 

 developed and possess numerous alveoli. 



In the vertebral column there are well-marked cartilaginous centra 

 and transverse processes. The cartilage of the neural arches reaches 

 almost to the summit of the cord. 



The diaphragm is only very slightly incomplete dorsally. The 

 oesophagus has a wide lumen throughout its length. The stomach 

 and some parts of the small intestine are full of a coagulum, pro- 

 bably milk, containing cells. The pancreas appears to be fully developed 



1) This curious fact was first recorded by Selbnka for the new- 

 born opossum. 



