124 BULLETIN OF THE ESSEX INSTITUTE. 



the anterior end of the cranial cavity and continues for- 

 ward into the roof of the nasal capsules. Ventrally a solid 

 plate of cartilage (<), the trabecular plate, forms a con- 

 tinuous floor beneath the anterior end of the cranial cavity 

 and the nasal capsules, and projects forwards as a short 

 and rather blunt rostrum (>). A small isolated plate 

 of cartilage (tc) occupies the middle of the supracranial 

 fontanelle, a remnant, as Pollard suggests, of a primitively 

 complete tegmen cranii. 



The nasal capsule consists of a large cavity enclosed by 

 simple, broad plates of cartilage. Its floor and roof are con- 

 nected by a tall septum medially and two bands laterally. 

 The posterior of these two bands marks the boundary be- 

 tween nasal capsule and cranial cavity. There are three 

 large apertures in the capsule walls : behind, the olfactory 

 foramen ; in front, the foramen for the nasal duct (nl) ; 

 and between them a third in the lateral wall. Besides these 

 there are two small foramina in the border of the nasal 

 roof, the 'canalis ethmoidalis' (ec) and the 'canalis pre- 

 orbitalis ' {pre). Dorsally these two are connected by a 

 deep groove. 



The anterior end of the palato-pterygo-quadrate car- 

 tilage {ppt) is applied to the ventro-lateral surface of the 

 nasal capsule. From here it passes backward as a broad- 

 ening band to a point beneath the outer wall of the otic 

 capsule and the hyomandibular cartilage. In passing from 

 in front backward it twists from an approximately hori- 

 zontal to a nearly vertical plane. 



The Trout {8ahno fontinalis) , (Figs. 28-29). 



For a representative of the Teleostean skull I have 

 modelled the chondrocranium of a trout embryo twenty- 

 two mm. in length. The occipital arch is fused with the 



