116 BULLETIN OF THE ESSEX INSTITUTE. 



The notochord occupies its usual position at the poste- 

 rior end of the cranium ; but, as it passes forward, it bends 

 downward so that its anterior end lies considerably be- 

 low the general level of the cranial floor. The para- 

 chordals are represented only by a narrow band of cartilage 

 connecting the posterior ends of the otic capsules. In 

 the median line the notochord is embedded in this band. 

 At its lateral margin the parachordal band fuses with the 

 occipital process behind and with the otic capsule in front. 

 The dorsal end of the occipital process is fused with the 

 otic capsule. Between these three cartilages is the jugu- 

 lar foramen {j) . 



The otic capsules are longer, narrower and deeper than 

 those of Ambly stoma, and, as is usual in the younger 

 stages, they are comparatively widely separated. In the 

 median wall of each capsule are two foramina, a larger 

 anterior and a smaller posterior foramen. The ventro- 

 lateral wall of the capsule is largely taken up by the fen- 

 estra ovalis along the dorsal part of which lies the stapes. 

 The stapes is continued forward into a process which 

 reaches the posterior surface of the quadrate. This pro- 

 cess may retain the name ' stapedial process,' although in 

 this case it is continuous with the stapes rather than with 

 the quadrate. The stapes is perforated in a dorso-ventral 

 direction for the arteria perforans stapedia (Fig. 23, as). 



Three processes arise from the anterior end of the otic 

 capsule. Two of these, which I shall call the dorsal {dr) 

 and ventral {vr) trabecular rods, extend forward in the 

 usual positions of the dorsal and ventral margins of the 

 trabecula. The third, and relatively much shorter process 

 is attached posteriorly to the otic capsule just below the 

 end of the dorsal trabecular rod. Curving downward and 

 forward it fuses with the ventral trabecular rod. In the 

 posterior end of the ventral trabecular rod there is a small 



