106 WEIL. . 



materially in size, and to assume the oval form seen in the model 

 (Plate III., Fig. 2). Beyond the dentary, it continues for a short 

 distance, unchanged in shape or direction, then gradually bulges 

 out at the end directed towards the base of the skull, and a 

 little later bends down at a sharp angle as in the Pig. This 

 highly differentiated portion without any doubt represents the 

 malleus ; in it may be distinguished, as seen in the model, head 

 (capitulum), neck (cervix), the processus gracilis, and the manu- 

 brium. Furthermore it has all the important relations of that 

 bone, impinging on the tympanic membrane, articulated with the 

 incus, etc. In direct continuity with it at some points, but al- 

 ready splitting off from it in others, is a relatively small cartilage, 

 the incus. The articulation between these two elements is of 

 the same nature as that found in the adult marsupial, and con- 

 trasts strongly with the ball and socket joint of higher mammals. 

 In the incus, the long crus to which the stapes is articulated, 

 and the short crus, contributed as in higher mammalia by the 

 auditory capsule (Dreyfuss), are easily to be distinguished. The 

 stapes is a single element, which comes into relation both with 

 the mandibular arch, through the long crus of the incus, and 

 with the periotic capsule. The stapes here appears as an im- 

 perforate plate, and the characteristic stapedial branch of the 

 carotid is lacking, so that the cause of its eventual perforation 

 in the adult still remains obscure. The hyoidean is attached, not 

 as in the Pig, in the proximity of the ear bones, but a measur- 

 able distance below them, so that this fruitful source of error 

 and confusion is eliminated. 



In a general way, the stage of development of the head is in- 

 dicated by the fact that the only bone present is the dentary. 



As regards the ossicula audita, the condition of the anlage 

 is very extraordinary, and presents a parallel v/ith no stage 

 found in the Placentalia. The cartilage of the bones in question 

 is already well formed, and their shape is accurately defined, as 

 in the Pig of from two to three inches, but in their relations to 

 other cartilages they present a far more embryonic condition 

 than is found even in the early stages in which these elements 

 can be made out in the Pig embryo, as above described. 



