ON THE THEORY OF THE VERTEBRATE SKULL 599 



just the same manner as the transverse processes of the three or four succeeding 

 caudal vertebrae. 



" If we consider, in the first place, the relation of the parts in the adult snake, 

 •we find that the penultimate rib, near its upper or inner end, gives off from its 

 upper side, a small process directed upwards and outwards ; however, in the last 

 rib this process is about a quarter as long as the remaining part of the rib, which 

 lies external to and below it, so that the whole bone has the form of a two-pronged 

 hay-fork, not yet fastened to a handle, and one of whose prongs is for the most part 

 broken off. The same fundamental form is possessed by the transverse process of 

 the first caudal vertebra ; and the difference between it, and the rib which lies 

 immediately before it, lies principally in this, that it is not, like the rib, articulated 

 with its vertebra, that its upper half or prong is almost equal in length to the 

 lower, and that, regarded as a whole, it is not half so long as the hindermost rib. 

 The transverse processes of the succeeding caudal vertebras have quite the same 

 form as their predecessors, but gradually diminish in length backwards. As to 

 the development of the ribs and transverse processes in question, they, like almost 

 all the other ribs, are originally sent out as quite simple rays from the bodies 

 of their vertebrae ; very soon, however, there arises on the upper side and neck 

 of the ray where it passes out from the vertebral body, an outgrowth which 

 elongates more or less, also assumes a ray-like form, and has its free end directed 

 outwards. Thus a fork is produced, whose one prong is more or less thicker than 

 the other." 



Rathke suggests that the accessory ribs of many fish are probably developed in 

 this way, the upper prong becoming articulated with the lower. 



" The two or three anterior subvertebral processes in the tail are, and remain, 

 quite simple, like the similar processes of the cervical and many dorsal vertebrae. 

 The two halves of the others, which arose as separate lateral processes, remain 

 permanently distinct. 



" All the newly commencing inferior processes arise as paired outgrowths of the 

 bodies of the vertebra." 



" The ribs are not less outgrowths iaiisstrahlicngen) of the bodies of the 

 vertebrae than the crura of the arches, as I can say from my investigations on 

 fishes, snakes, lizards, birds, and mammals ; even when the bodies of the vertebrae 

 are completely chondrified, the ribs form a connected whole with them, but 

 subsequently they become articulated, and are thereby essentially distinguished 

 from the crura of the vertebral arches. In some animals the articulation takes 

 place and remains close to the bodies ; in others it takes place also close to the 

 bodies, yet, afterwards, a process grows out between the rib and the body, by 

 which the rib is more or less thrust out ; this is the transverse process ; where 

 it occurs, the rib is, in all cases, at first united only with it ; sometimes, however, 

 a process grows out from the rib (the so-called head with its neck), by which it 

 becomes immediately attached to the body of the vertebra itself, so that it is 

 doubly united with the body. In many cases the rib may also become articu- 

 lated at some distance from the body, and thus break up into rib and transverse 

 process." 



"As respects the ribs of the higher Ver/ei>raUz, together with their transverse 

 processes, the development of the snake teaches us, that although they are 

 subsequently seen to be in close connexion with the crura of the vertebral arches, 

 they grow out, not from the base of these arches, but far from them, out of the 

 bodies of the vertebrae themselves ; where they have arisen, however, each lateral 

 half of the body of the vertebra increases in thickness, in such a manner that 

 it acquires an ala, which drives the crus of the vertebral arch and the rib further 



