284 report — 1846. 



chelonians, the ichthyic independence af the parapophyses (4, 4). In batra- 

 chians the epencephalic arch is reduced to the two important elements, the 

 neurapophyses ; which meet and join each other below as well as above the 

 foramen magnum, and develope the exogenous zygapophyses, or two occipital 

 condyles, for articulation with the corresponding processes of the neural arch 

 of the atlas. The basioccipital, if it exists in batrachians, is rudimental and 

 confluent with the basisphenoid, and the supraoccipital is in like manner 

 recognisable only as the posterior border of the backwardly produced parietal. 

 The parapophyses are short exogenous processes of the neurapophyses of this 

 much simplified epencephalic arch in all batrachian reptiles. 



The chief modification that distinguishes the above-described segment of 

 the crocodile's skull from its homologue in the fish, is the absence of an 

 attached inverted or haemal arch. We recognise, indeed, the special homo- 

 logues of the piscine constituents of that arch in 50, 51 and 52, fig. 22. The 

 upper suprascapular piece (50) is however free, disconnected from any seg- 

 ment, and retains, in connection with the loss of its proximal or cranial 

 articulations, its cartilaginous state : the scapula (51) is ossified, as is likewise 

 the coracoid (52), the lower end of which is separated from its fellow by the 

 interposition of a median, symmetrical, partially ossified piece called 'epister- 

 num ' (hs). The power of recognising the special homologies of 50, 51, and 

 52 in the crocodile, with the similarly numbered constituents of the arch H 1 

 in fishes (fig. 5), though masked not only by modifications of form and pro- 

 portion but even of very substance, as in the case of 50, depends upon the 

 circumstance of these bones constituting the same essential element of the 

 archetypal skeleton : for although in the present instance there is superadded 

 to the adaptive modifications above cited the rarer one of altered connections, 

 Cuvier does not hesitate to give the same names (suprascapulaire) to 50 

 and (scapulaire) to 51, in both fish and crocodile : but he did not perceive or 

 admit that the narrower relations of special homology were a result of, and 

 necessarily included in, the wider law of general homology. According to 

 the view of this law here taken, we discern in 50 and 51, fig. 22, a teleologically 

 compound pleur apophysis, in 52 a hcemctpophysis, and in hs the haemal 

 spine, completing the haemal arch. 



The general relations of the scapulo-coracoid arch to a haemal or costal 

 one have been long recognised, but the vertebral segment to which it apper- 

 tains seems not hitherto to have been suspected, and has certainly not been 

 satisfactorily determined. Oken, who had observed the free cervical ribs in 

 a specimen of the Lacerta apoda, Pallas (Pseudopus), deemed them repre- 

 sentatives of the scapula, and this bone to be, in other animals, the coalesced 

 homologues of the cervical pleurapophyses*. In no animal are the conditions 

 for testing this question so favourable and obvious as in the crocodile : not 

 only do cervical ribs coexist with the scapulo-coracoid arch, but they are of 

 unusual length and are developed from the atlas as well as from each suc- 

 ceeding cervical vertebra : we can also trace them beyond the thorax to the 

 sacrum, and throughout a great part of the caudal region, as the sutures of 

 the apparently long transverse processes of the coccygeal vertebrae demon- 

 strate in the young animal; the lumbar pleurapophyses being manifested 

 at the same period as cartilaginous appendages to the ends of the long dia- 

 pophyses. 



* " Auch die Scapula nicht em Knochen, sondern wenigstens eine aus fiinf Halsrippen 

 zusammengeflossene Platte ist." — Programm, &c, 4to, 1807, p. 16. He reproduces the 

 same idea of the general homology of the scapula in the ' Lehrbuch der Natur-philosophie,' 

 1843, p. 331, If 2381. Cams also regards the scapulo-coracoid arch as the reunion of seve- 

 ral (at least three) protovertebral arches of the trunk-segments. ' Uitheilen des Knochen 

 und Schalen gerustes, fol. dxliii. 



