290 report— 1846. 



rietal centrum (5). The neural spine of the frontal vertebra (xi) retains its 

 normal character as a single symmetrical bone, like the parietal spine, which 

 it partly overlaps. It is much developed longitudinally, but more in the 

 anterior, and less in the lateral direction than in most fishes. 



One cannot contemplate the relative position of the frontal to the parietal 

 and of the parietal to the supraoccipital, which is overlapped by the parietal 

 and itself overlaps the flattened spine of the atlas, without a conviction of the 

 serial homology of these single, median, imbricated bones, all completing 

 arches above the neural axis, and each permanently distinct from the piers 

 or haunches of the arch of which it forms the key-stone. In like manner 

 the serial homology of those piers or neurapophyses, viz. the laminae of 

 the atlas, the exoccipitals, the alisphenoids and the orbitosphenoids, is equally 

 unmistakeable. Nor can we close our eyes to the same serial relationship 

 of the postfrontals (fig. 20, 12, 12) as parapophyses of their vertebra, with 

 the mastoids (s) and the coalesced paroccipitals (4). The frontal parapo- 

 physis, 12, is wedged between the back part of the spine, 11, and the neur- 

 apophysis, 10 : its outward process extends backwards and joins the next 

 parapophysis (s) ; but, notwithstanding the retrogradation of the mandi- 

 bular arch, it still receives a small part of its own pleurapophysial element 

 (2s). This element now manifests its typical unity : vegetative subdivision, 

 much reduced in the batrachian reptiles, no more prevails in the develop- 

 ment of the frontal pleurapophysis in any higher vertebrate. The serpents 

 exhibit this element under the common form of a rib ; longer, indeed, than 

 are any of the pleurapophyses in the batrachian order ; but it has so far 

 retreated in serpents as to be exclusively attached to the parietal parapo- 

 physis, which is remarkably elongated and produced backwards, and sus- 

 pends the long, slender, straight and simple frontal pleurapophysis (tympanic 

 pedicle) vertically from its posterior extremity. In lacertians no. 28 is ver- 

 tically suspended from no. 8, and, commonly also, from no. 27, which is con- 

 tinued from the backwardly produced parapophysis of the frontal vertebra 

 (12) to that of the parietal vertebra (s) in most of this division of the Cu- 

 vierian order Sauria. In chelonians and crocodilians the diverging appen- 

 dage of the maxillary arch (27) descends and applies itself to a large propor- 

 tion of no. 28, down to its lower articular end, and contributes to fix and 

 strengthen that bone, as well as the modified costal arch from which it di- 

 verges. 



The condition of the shortening, expansion and fixation of the frontal 

 pleurapophysis in crocodiles and chelonians is exemplified in the uses to 

 which the modified haemapophyses, completing that costal arch, are put. 

 Tortoises crop the grass by the application of the trenchant horny plates of 

 the under to those of the upper jaw : turtles equally need a fixed suspensory 

 joint of the under jaw in the act of biting and dividing the tough sea-weeds. 

 Crocodiles have the frontal haemapophyses (mandibular rami) unusually 

 long ; supporting numerous large laniary teeth, and requiring a fixed and 

 firm point of suspension in the violent actions to which they are put in re- 

 taining, and overcoming the struggles of their prey. 



The teleological complication of the lower or distal elements of the arch 

 in question (29-32, fig. 22) is carried further than in fishes : there was more 

 need, in fact, for a combination of the greatest elasticity and strength with 

 the least weight of bone* in the frontal haemapophysis of the crocodile than 

 in the frontal pleurapophysis of the fish (2s a-28 d, fig. 5). 



There, lastly, remain then in the skull of the crocodile the bones inter- 



* Conybeare, Geol. Trans. 1821, p. 565. Buckland, Bridgewater Treatise, 1836, vol. i. 

 p. 176. This author well illustrates the final purpose of the subdivision of the mandibular 



