142 MR. W. K. PARKER ON THE STRUCTURE 



Standing in the ways to see and to judge which is the right path for each Carinate 

 type, the worker finds it no " far call " from the order-joining Tinamous to the Plovers on 

 one hand, and the Fowls on the other. 



The sucker which grows into the Passerine tree is not so clearly discernible in the 

 Tinamine stock — in such Tinamous as now exist ; but just above where the fork is, the 

 Hemipods are unmistakable in their relation to the harsh -voiced Passerines of the southern 

 hemisphere. 



Above, when the Tinamine branch forks amongst types of no great elevation, and in 

 which the Droinaeognathous skull has passed into the Schizognathous, we see the nobler 

 forms (" Aves aeriae") just superimposed upon and, as it were, growing from the lower 

 forms — the " Prsecoces." 



Prom above the Sand-Plover arose the Pigeon, in its older and now extinct forms ; 

 and from above old types of the Gallinacese the fundamental or stock-form of the Rapa- 

 cious bird sprung. The genus Dicholophus is but little changed from such a primitive 

 plunderer. 



Skull of Gavia ridibunda. 1st stage. 



There were five stages of the young of the Laughing-Gull amongst those examined by 

 me ; to these are added the adult ; the largest young were just ready for flight, the 

 smallest only about a week old. 



After these had been worked out, I obtained half-ripe young of the Silvery Gull 

 (Larus argentatus) from the " Lesser Orme's Head," near Llandudno ; but these, although 

 studied in various ways, have not been wholly worked out by me ; their condition at that 

 early stage differs but little from embryos of the Common Powl (see Phil. Trans. 1869, 

 plate lxxxii., 3rd stage). 



In the first stage the primordial skull (chondrocranium) is thoroughly formed ; it has 

 also most of the osseous centres commenced, and some of them ankylosed to their neigh- 

 bours. The occipital region is very instructive ; the basiocciptal (Plate XXVI. fig. 2, bo) 

 is a long oval piece, enclosing the starved notochord, and separated by large cartilaginous 

 tracts from the lateral pieces, the exoccipitals (eo). These bones are very irregular 

 pentagons ; they are creeping over the hinder part of the auditory capsule, the canals of 

 which are seen shining through the clear cartilage (figs. 1-3, hsc, psc). The ex- 

 occipitals already half enclose the foramen magnum (fin) ; but a good space exists between 

 them and the double keystone piece, the superoccipital (so). This latter bone is com- 

 posed of two halves, which are only half-soldered together ; above they are quite distinct. 

 They now form a very elegant bony plate with many sides, some having a scooped and 

 others a rounded outline. 



The archway of the foramen magnum is finished by the concave margin of the 

 coalesced part ; above, behind, and below the parietals (p), the margin is a bifoil. 

 Between these margins the bone has an indrawn waist ; on each side, at this part, there 

 is a non-cartilaginous space — a " fenestra " or " fontanelle," the lateral occipital fon- 

 tanelle so familiar to osteologists in Pluvialine and Anserine types (see in Vanellus 

 cristatus, Trans. Zool. Soc. vol. v. plate xxxvii. figs. 1, 2, & 4, I. o.f). 



