98 BULLETIN OF THE ESSEX INSTITUTE. 



by bone. At the same time the whole skull has increased 

 in breadth as compared to its length. 



The synotic tectum (Fig. 12, st) is completely sepa- 

 rated from the remnants of cartilage formins: the otic 

 capsules, and the basilar plate Q9) is reduced in length to 

 little more than that of the tectum. Ossification has re- 

 moved nearly all of the cartilage of the capsule behind the 

 posterior end of the fenestra ovalis where the stapes is 

 now closely applied against the remnant of the cartilagi- 

 nous wall of the capsule. 



The quadrate (q) has undergone important changes, 

 due in part to ossification and to the lateral expansion of 

 the skull. Its body is thicker antero-posteriorly and 

 stands out farther from the capsule. The descending 

 process is cylindrical in shape, presenting greater definite- 

 ness of outline than previously. Irregular perforations 

 of the cartilage occur along the line where the quadrate 

 joins the capsule. Most striking of all is the change 

 in the position of the pterygoid process (pt) which, in- 

 stead of being nearly parallel with the long axis of the 

 skull as in the previous stage, now slants from its base 

 outwards at an angle of about thirty degrees from that 

 axis. 



The cartilaginous nasal capsules have reached their 

 highest stage of development and present many new and 

 important features. The nasal septum (Fig. 12, 7is) is nar- 

 rowed down to about half its former width. In front it 

 divides into two doubly curved plates which extend for- 

 wards and outwards to the cup-like anterior ends of the 

 capsules. From the ventro-median surface of each of 

 these plates a short knob-like process extends forwards and 

 terminates the capsule anteriorly. 



A flattened band of cartilage which I have called the 

 ventral process (vp), in contradistinction to the dorsal 



