118 BULLETIN or THE ESSEX INSTITUTE. 



tance in front of the distal portion of the pterygoid is 

 another isolated rod of cartilage which runs in a direction 

 diagonal to tbat of tiie pterygoid process. This is the 

 palatine cartilage (pc). 



Meckel's cartilage articulates with the ventral surface 

 of the body of the quadrate. Anteriorly the cartilages of 

 the two sides are still separated. They project backward 

 behind the point of articulation with the quadrate nearly 

 as far as the posterior end of the stapes (a). 



Second stage. — (Figs. 24-26). — The parachordals 

 and occipital processes are in the same condition as before, 

 there being no trace of the formation of a synotic tectum. 

 The notochord has entirely disappeared from the head 

 region. The median wall of the otic capsule is more com- 

 plete than it was in the first stage (Fig. 25). What was 

 then the large anterior foramen is now divided into a 

 dorsal foramen for the endolymphatic duct (ef) and a 

 large ventral foramen for the auditory and facial nerves. 

 The floor of the capsule is now composed of a median and 

 a more lateral rod between which a fontanelle is enclosed. 

 The stapes and fenestra ovalis are in the same condition 

 as in the preceding stage. 



The rod described in the first stage as connecting the 

 anterior end of the otic capsule with the ventral trabecular 

 rod now has a nearly vertical direction, the ventral end 

 being relatively more posterior in position than before. 

 As far forward as the orbital region there are no other 

 noteworthy changes. In the nasal region, howevei', im- 

 portant changes have occurred. Instead of the trans- 

 versely expanded nasal region of the earlier stage, we now 

 find the anterior ends of the dorsal trabecular rods folded 

 inward toward the nasal septum and forming a roof over 

 the sides of the olfactory organs. By this movement the 



