ON THE VERTEBRATE SKELETON. 221 



the same figures, to which the name of 'anterior frontal' is given, have no 

 relation whatever to the protection of the rhinencephala or the exit of the 

 olfactory nerves, but they have a large perforation for the passage of the 

 muco-lacrymal duct from the eye. They repeat indeed the single and 

 least essential character of the prefrontals, in standing anterior to the fron- 

 tals and the orbits ; but these are characters common to the great anterior 

 mucous scale-bone in fishes, whose essential function — the transmission of a 

 mucous duct — they superadd to the repetition of its connections, viz. with 

 the prefrontal, nasal and superior maxillary bones*. 



The bones, which more resemble the anchylosed prefrontals in the frog, are 

 the frontals of the python ; but the resemblance is confined to one character 

 only, and that an exaggeration of a character common to the frontal bones of 

 many birds, and of the ornithorhynchus among mammals, viz. a develop- 

 ment of a median bony partition from the line of the frontal suture into the 

 median interspace of the encephalon. In the python each frontal sends 

 down at the fore-part of this suture such a partition, which is therefore double, 

 as the falx essentially is in man and the mammalia, in which it retains its 

 primitive histological condition of a fibrous membrane. The ossified laminae 

 of the falx in the python bend outwards and coalesce below with the external 

 or orbitosphenoidal plates of the frontal, and thus surround the lateral divi- 

 sions of the fore-part of the brain ; in fact, the olfactory nerves, drawn back 

 in the progress of the concentrative movement of the cerebral centres, so as 

 also to occupy the prosencephalic segment of the cranium, the prosencepha- 

 lon being, in like manner, protected chiefly by the mesencephalic bony arch. 

 The change is precisely analogous to that which takes place at the opposite 

 extremity of the neural axis in higher animals. In the python every segment 

 of the spinal chord retains its primitive relation to the segment of the en do- 

 skeleton, through which it transmits its pair of nerves. In the mammal the 

 concentrative movements of the spinal chord draw its segments in advance 

 of their proper vertebrae, and the primary relation is indicated by the nerves 

 which these vertebrae continue to transmit, and by which alone we are guided 

 from the segment of the endoskeleton to that of the neural axis which origi- 

 nally governed its development. 



So, likewise, at the opposite end of the skeleton, we trace the relation of 

 the anterior osseous segment, which transmits the olfactory nerves to their cap- 

 sule, to its proper segment of the neural axis, by following those nerves back 

 to the retracted ganglions (rhinencephala) from which they take their origin. 

 The connections of the annular frontals of the python with the parietals 

 and post-frontals behind, with the connate orbitosphenoids, and through 

 them with the presphenoid below, prevent their homology being mistaken ; 

 for they are far from completely representing or repeating the essential cha- 

 racters of the coalesced annular prefrontals of the frog. 



Not to lengthen unnecessarily this exposition of the homologues of the pre- 

 frontals (14, figs.4 and 5) in fishes, I pass at once to the highest of existing rep- 

 tiles, the crocodile. Here we find, in the dry skull, the condition of the cranial 



* No one could better appreciate the value of the functional character of the lacrymal 

 perforation in a homological discussion than Cuvier, when the more obvious features of the 

 prefrontals of fishes were so repeated in any higher animal as to have led him to distinguish 

 the prefrontals in that animal from the lacrymal bone. Thus with regard to the pre- 

 frontals of the crocodile, Cuvier says, " Quant a, M. Spix, entraine par un autre systeme et 

 negligent le trou lacrymal, qui cependant est bien visible, et qui, specialement dans le cro- 

 codile, est perce tout entier dans l'os auquel je donne ou plutot auquel je maintiens le meme 

 nom, c'est mon frontal anterieur qu'il appelle lacrymal." (Ossemens Fossiles.) Change 

 python for crocodile and Cuvier for Spix, and the criticism equally applies in the present 

 instance to its original author. 



