262 MR. W. K. PARKER ON THE STRUCTURE AND 



In Rana pipie^is there are two or three splint bones [inter-suspensorials) between 

 the quadrate cartilage and the hind cms of the pterygoid bone. 



In some t;y'pes (e.g., Ceraiojjhrys, Cahjptoceplmlus, Pdohates, and Nototremd) the 

 surface of the investing bones is ornate, and almost Ganoid. 



The following endoskeletal and exoskeletal bones are constant throughout the 

 " Anura " in the adult skull :— 



1. The ex-occipitals.* 



2. The prootics. 



3. The pterygoids. 



4. The articidars. 



5. The thyro-hyals. 



6. The parasphenoid. 



7. The nasals. 



8. The fronto-parietals. 



9. The premaxillaries. 



10. The maxillaries. 



11. The squamosals. 



12. The dentaries. 



The skull is always finished with cartilage, below (contrary to the Urodeles), and 

 never finished with cartilage, above (as in the Shai-ks). 



The occipital condyles are always double, and quite distinct, often wide apart ; but 

 the occipital arch is not always restricted to a right and left bone ; thei-e may be a 

 rudiment, above and below, of a median centre. 



The skull is always closed in front by the ethmoid (cartilage or bone) : it is at 

 times very unfinished and membranous in the orbital region (e.g., liappia bicolor, 

 Camariolius tasmaniensis, and Acris Pickenngii). 



The whole (true) ethmoidal region is formed by the trabeculse and intertrabecula ; 

 the nasal roofs are distinct cartilages at first (like the eye-balls and auditory capsules) ; 

 their floor is formed by the trabecidai. 



F. — On the likeness and unlikeness of the skulls of the " Urodela" and "Anura." 



The difference between the skull of a Tadpole and that of a larval Urodele is very 

 great from the first (see Phil. Trans., 1877, Plates 22-24). In the latter the tra- 

 becules largely embrace the huge cranial notochord, and are some time before they 

 close in in front of the membranous space below the fore brain. They finish their 

 cornua, in the internasal region, afterwards, and they do not finish the occipital floor ; 

 distinct parachordals appear there. 



The suspensorium is in them, at first, quite distinct from the trabecula, when it does 

 coalesce it unites, first, with the wall of the skull, above the orbito-nasal nerve ; in the 

 Tadpole it is from the first continuous, as cartilage, below that nerve. Their ethmo- 



* Tho prootics aud c.\-occipital.s do not always arise from iiuk'|>eudt'nt centres. 



