126 BULLETIN OF THE ESSEX INSTITUTE. 



cranial cavity. This cranial roof is fused anteriorly with 

 the dorsal end of the nasal septum (Fig. 28, ns.) In its 

 anterior end there are three apertures, a median fontanelle 

 and two small lateral foramina, through each of which 

 passes a branch of the ophthalmicus superficialis (rs). A 

 band of cartilage connecting the tegmen cranii and the 

 dorsal end of the septum with the lateral border of the 

 ethmoid plate separates the nasal region from the cranial 

 cavity. There is no cartilaginous roof or lateral wall to 

 the nasal capsule. The septum is thick and slightly ex- 

 panded dorsally and in front where it ends bluntly. 



The anterior end of the pterygo-quadrate cartilage is 

 applied to the ventro-lateral margin of the ethmoid plate. 

 From here it extends backward as a slender rod to be- 

 neath the anterior end of the otic capsule where it broad- 

 ens into an irregular plate with an articular process 

 ventrally for the attachment of Meckel's cartilage. Its 

 posterior end is connected with the otic capsule by means 

 of the plate-like hyomandibular cartilage (h). The dor- 

 sal margin of this cartilage, the hyomandibular, lies 

 closely pressed against the external surface of the otic 

 capsule just beneath the horizontal canal. It is broad 

 and thin above and narrower and thicker below. From 

 its ventral end a long rod-like process runs forward be- 

 neath the posterior end of the pterygo-quadrate, reaching 

 almost to the point of articulation with Meckel's cartilage. 

 The hyomandibular branch of the seventh nerve passes 

 through a foramen just above the middle of this cartilage 



The Chondrocranium in the Fishes. 



The chondrocrania of the two types of this group 

 which have been described have many features in com- 

 mon, and it seems probable that a comparison of corres- 



