PEOF. W. K. PAEKEE ON .EGITHOGNATHOUS BIEDS. 313 



gidte ;" and the nearly perfect hinge is bounded in front by a knife-like septum, as in 

 St/rrhaptes, Hemipodius, and Faclnjrliamphus ; but this is not ossified ; it is not alate in 

 the middle, but has in front two triangular laminae of bone underpropping it ; the lower 

 of them is a median process of the prsemaxillary ; and the higher is the " recuiTent 

 lamina " of the trabeculse {re. c) ; this is largely edged by unossified cartilage. 



In Thamnophilus we have a pertinent instance of the occurrence of intense ossification 

 in a low type, showing that arrest of ossification is not of itself a sign of low position'. 

 The whole nasal capsule is ossified, with the exception of the margin of the very large 

 recurrent laminse and the septum, and had better be considered along with the vomerine 

 structures. 



The alinasal turbinals (a. tl) are very large and bony, and they articulate by their 

 convex end with a concavity on the horns of the enlarged vomer (fig, 9, a. tb, v). The 

 alinasal wall(«/.M) is not even fl:ush with the facial bones (fig. 10), but sinks in, and is 

 thoroughly ossified ; below and within it is seen to have coalesced completely with the 

 maxillo-palatine process (fig. 9, i. a. I, mx.p), and is of very small extent in the floor of 

 the nose, which is here open, exposing the alinasal and inferior turbinals {a. tb, i. tb). 

 Here the bony growths are much in conformity with the morphological regions, save 

 that the ankylosis of the alee nasi with the palatine plate of the maxillary has produced 

 a form of desmognathism. 



In Thamnophilus the vomerine moieties are as much indebted to hyaline cartilage for 

 the formation of their wings and crests as in the Crow, but the source is diff'erent : here 

 the cartilage is the vomerine spatula ; there, in the Crow, that cartilage is soon used up, 

 and then the bone grows into the nasal capsule to a certain extent. In this instance the 

 vomerine cartilages are themselves large enough to form a substratum for all the out- 

 growings of the vomer, so large and massive in the adult. 



Not only does the alinasal turbinal form a cup-and-ball joint with the vomer, but the 

 vomer itself has an elevated subconvex facet on each side, which fits into a subroncave 

 facet on the upper surface of the corresponding maxillo-palatine plate. Altogether this 

 segithognathous palate is developed into a very complex kind of desmognathism. 

 At first sight the septum would seem to be ossified ; but a side view shows that it is 

 only the inferior edge which is bony, and the bone is quite free from the cartilage ; it is, 

 in this state, merely a membrane bone, a " median septo-maxillary " (fig. 8, m. s.nw). 

 We shall soon meet with this element again. 



The preemaxillaries form the strong, narrowish, decurved beak, and are thoroughly 

 ankylosed to their surroundings. 



The pterygo-palatin€ arch has a typical apex, the epipterygoid hook (e.pg) ; it is longer 



than is usual even in the higher forms. The pteiygoids are rather long, elegantly bowed, 



and have given off a large mesopterygoid, which has become ankylosed to the upper edge 



of the palatine ; the pterygoids remain distinct. The palatines are extremely like those 



' Neither intense ossification nor pneumaticity of the bones ar« signs of " high degree." 



VOL. IX. — PAET v. December, 1875. 2 v 



