CROCODILIA. 



25 



The bone anterior to the orbit, marked 73 in fig. 9, and in T. I and T. VI is perforated 

 at its orbital border by the duct of the lachrymal gland, whence it is termed the 

 'lachrymal bone,' and its facial part extends forwards between the bones marked 

 14, 15, 21, and 26 in the same plates. In many Crocodilia there is a bone at the 

 upper border of the orbit, which extends into the substance of the upper eyelid ; it is 

 called c superorbital.' In the Crocodilus palpebrosus there are two of these ossicles. 



Both the lachrymal and superorbital bones answer to a series of bones found com- 

 monly in fishes, and called ( suborbitals' and ' superorbitals.' The lachrymal is the 

 most anterior of the suborbital series, and is the largest in fishes ; it is also the most 

 constant in the vertebrate series, and is grooved or perforated by a mucous duct. 

 These ossicles appertain to the dermal or muco-dermal system or ' exoskeleton.' 



The little slender bone, marked 16' in fig. 9, has one of its extremities in the form 

 of a long, narrow, elliptic plate, which is applied to the ' fenestra ovalis' of the internal 

 ear ; from this plate extends a long and slender bony stem, which grows somewhat 

 cartilaginous, expands and bends down, as it approaches the tympanum or ear-drum, to 

 which it is attached. 



The cartilaginous capsule of the labyrinth or internal ear is partially ossified 

 by sinuous plates of bone connate with the neurapophyses (fig. 10, 2 and 6), between 

 which that organ is lodged ; I apply the term ' petrosal' to the principal and most 

 independent of those ossifications of the ear-capsule, to that, e. g., which retains 

 some mobility after it has con- 

 tracted a partial anchylosis to 

 the exoccipital (2), and which 

 appears upon the inner surface 

 of the cranial walls at the part 

 marked 16 in the subjoined 

 Cut 10, between 2 and 6. It 

 is the only independent bone 

 on that surface of the cranium 

 which, in my opinion, answers 

 to the ' petrous portion of the 

 temporal' in human anatomy, 

 and to which the term 'rocher 

 can be properly applied, in the language of the French comparative anatomists. Cuvier, 

 however, restricts that name to the ' alisphenoid' (6, figs. 9, 10) in the Crocodiles. 



The ossicles, (16 and 16', fig. 9), together with the partial ossifications in the sclerotic 

 capsule of the organ of sight, (17, fig. 9) — always more distinct in Chelonia than in 

 Crocodilia — belong to that category of visceral bones to which the term ' splanchno- 

 skeleton' has been given ; they also are foreign to the true vertebrate system of the 

 skeleton. 



4 



Fig. 10. 



Vertical longitudinal section of the cranium of a Crocodile 

 {Crocodilus acittus). 



