114 ME. W. K. PAEKEE ON THE STEUCTUEE AND 



Amphibians, Snakes, Lizards, and Birds, is a mere palatine outgrowth of the maxil- 

 lary in Crocodiles and Mammals ; working ascendingly, I call this bone (mistaken by 

 CuviER and most others for a " turbinal ") simply the " prevomer." 



A similar instance is not far to seek ; for the palatine plate of the palate-bone of the 

 Crocodile and Mammal is in certain Birds {e. g. the " Lamellirostres ") a small but 

 distinct ossicle; this I have called " interpalatine." On the whole, however, I have 

 endeavoured to keep very close to the old familiar human-anatomy terms, eschewing 

 meanwhile all those synonyms which appear to me to mislead the student who is in 

 search of true morphological unity. 



For opportunities of studying very many valuable specimens that I could not have 

 otherwise seen, I have to thank the Council and Officers of the Royal College of Sur- 

 geons — especially Mr. W. H. Flower ; and also Dr. Sclater and the other Officers of 

 the Zoological Society. 



Nor must I forget to state that throughout my work I have constantly had the great 

 advantage of the advice and cooperation of my friend Professor Huxley. 



The Skull of the Great Ostrich (Struthio camelus, "A."). 



For a description of the earliest stages of growth in the Bird's skull I must refer the 

 reader to Professor Huxley's new work on the ' Elements of Comparative Anatomy,' 

 pp. 130-142, fig. 57, A-F'. 



My youngest struthious embryos are those of the African Ostrich {Struthio camelus) ; 

 two of these were scarcely larger than a sparrow ; but the head of each was 1^ inch 

 long, whilst the shanks measured only 9 lines. 



At this stage (" Struthio, A") the cartilaginous skull is perfectly formed (Plate VII.), 

 and a few of the bones which develope in it have appeared ; there is no trace, however, 

 of some very important of these bone-patches. On the other hand, the calcareous sub- 

 stance has begun to harden those dense webs of fibrous tissue which are destined to 

 form the secondary bones, viz. those which have no preexisting hyaline cartilage. A 

 considerable part of the primordial skull is a long time before it ossifies ; some of it 

 does not ossify at all ; and some very important parts — the anterior third of the coalesced 

 " trabeculse cranii " and the anterior or lower two-thirds of " Meckel's cartilages " — are 

 absorbed soon after hatching. 



As a rule, the secondary bones (opercular bones, splint bones) appear first ; they are 

 not formed at random, but the fibrous matrix which becomes osseous tissue is in some 

 degree separated into bone-territories by the intervention of somewhat looser tracts of 

 connective tissue. It seems to be quite certain that the diaphysial osseous deposit, even 

 in cartilage-bones, is at first quite external to the cartilage-cells and their progeny, and 

 even to the intercellular substance which binds them into one clear, cheese-like mass. 



But the connective tissue which enwraps hyaline cartilage (perichondrium) is at one 

 time internal, and at another time external to the first laying in of phosphate of lime. 

 This gives us a most important fundamental distinction between primary and secondary 



