OF THE SKULL IK LEPIDOSTEUS OSSEUS. 
48r 
Ill the Salmon “ fry ” there is a hinder and a front tegmen cranii, a pair of super- 
orbital bands running from the auditory capsules to the anterior tegmen, a largely open 
roof between, open orbito-sphenoida] spaces, and an open pituitary fontanelle. More¬ 
over, this is the “ norma ” according to which the skull of Polypterus is formed; but of 
course during growth it becomes more solid, and partly ossified. 
The suspensorium suggests a very mixed relationship in this type ; it runs forwards, 
parallel with the skull, as in the Tadpole, but its pedicle is now well articulated with 
a basipterygoid process as in the metamorphosed Frog, and more clearly than in that 
type prefigures the cranio-facial relation of the Sauropsida, where, as in Lizards and 
many Birds, the pterygoid portion of the suspensorial apparatus articulates with a 
basipterygoid outgrowth of the skull. The open orbito-sphenoidal spaces are seen 
again in Batrachians, e.g., in Acris Pickeringii and Ra/ppia bicolor. 
The palatine portion of the suspensorium (or palato-quadrate cartilage) loses its 
ethmoidal conjugation, but retains its continuity with the pterygoid cartilage. The 
primarily and permanently separate palatine of the “ Siluroids ” runs forwards in the 
same manner, with no ethmo-palatine joint, such as is seen in the Salmon. 
In adult Batrachians of the genus Bufo the continuity of the palatine cartilage is lost 
both with the ethmoid and the pterygoid cartilage, but it articulates with the former 
by a raised process as in the Salmon. The small size of the hyomandibular of Lepi- 
dosteus, and its distance from the mandibular pier, prepare us for the transformations 
of that part in the Batrachia where it becomes the “ columella.” 
In a further stage, when it has doubled the size it had in the last instance—has 
become 2 inches long—the young Lepidosteus has fairly attained to its own charac¬ 
teristic type of skull, and most of the very limited osseus centres are now apparent. 
All the fore face is now greatly drawn out, twice as much as in the last, and the 
suspensorium, mandible, and lingual cartilages, have shot on forwards in like manner. 
The membranous spaces are only different from the last by the upper fontanelle being 
relatively less, and neatly circular, whilst the lower space is being divided by a late 
and feeble “ post-pituitary ’’ bar with a large anterior, and a small posterior space. But 
the type of skull seen in the young “ fry ” of the Salmon, and in such minute arrested 
Frogs as the Nearctic Acris Pickeringii , and the Australian Rappia bicolor and 
Camariolius tcismaniensis, is not departed from, nor, indeed, will be. 
But even what is seen in young Lepidostei 2 inches long scarcely prepares us for 
■what we find in specimens a little more than twice that size. At this stage, as in Saw¬ 
fishes ( Pristis ), this prenasal cartilage (intertrabecula) has become three times as long as 
the whole cranial cavity, and six times as long as its associated cornua trabeculae—now 
mere delicate leafy appendages to its base. The cranium proper has not altered in any 
important degree since the last stage, but the bony centres are nearly all there; all 
those that are seen in the Salmon, or in Teleostei, generally are found, with the 
exception of the super-occipital and a bone not found, I believe, in the Ganoids, 
namely, the “ pterotic;” its suppression is correlated with the development of a special 
MDCCCLXXXII. 3 R 
