102 BRITISH FOSSIL REPTILES. 



With reference, therefore, to the occipital vertebra of the crocodile, if the com- 

 paratively well-developed and permanently distinct ribs of all the cen'ical vertebrae 

 prove the scapular arch to belong to none of those segments, and, if that hjemal arch l^e 

 required to complete the occipital segment, which it actually does complete in fishes, then 

 the same conclusion must apply to the same arch in other animals, and we must regard 

 the occipital vertebra of the tortoise as completed below by its scapulo-coracoid arch 

 and not, as Bojanus supposed, by its hyoidean arch.* 



Having thus endeavoured to show what the scapular arch of the crocodile is, I 

 proceed to point out the characteristic form of its chief elements. The upper and 

 principal part of the scapula (.51, fig. 13) is flattened, and gradually becomes narrower to 

 the part called its neck, which is rounded, bent inwards, and then suddenly expanded to 

 form a rough articular surface for the coracoid, and a portion of a smoother surface for the 

 shoulder-joint. The contiguous end of the coracoid (52) presents a similar form, having 

 not only the rough sui'face for its junction with the scapula, but contributing, also, one 

 half of the cavity for the head of the humerus. It is perforated near the interspace 

 between these two surfaces. As it recedes from them, it contracts, then expands and 

 becomes flattened, terminating in a somewhat broader margin than the base of the 

 scapula, which margin is morticed into a groove at the anterior border of the broad 

 rhomlwidal cartilage continued beyond the ossified part of the manubrium, which forms 

 the key-bone of the scapular arch. The anterior locomotive extremity is the 

 diverging appendage of the arch, under one of its numerous modes and grades of 

 development.f 



The proximal element of this appendage or that nearest the arch, is called the 

 ' humerus' (53, fig. 13) : its head is subcompressed and convex; its shaft bent in two 

 directions, with a deltoid crest developed from its upper and fore part ; its distal end 

 is transversely extended, and divided anteriorly into two condyles. The shaft of 

 this bone has a medullary cavity, but relatively smaller than in the mammalian 

 humerus. 



The second segment of the limb consists of two bones : the larger one (54) is called 

 the ' ulna :' it articulates with the outer condyle of the humerus by an oval facet, the 



* Anatome Testudinis Europpea, fol., 1S19, p. 44. GeofFroy St. Hilaii-e selected the opercular audsub- 

 opercular bones to form the inverted arch of his seventh (occipital) cranial vertebra, and took no account of 

 the instructive natural connexions and relative position of the hyoidean and scapular arches in fishes. With 

 regard to the scapular arch, he alludes to its articulation with the skull in the lowest of the vertebrate 

 classes as an ' amalgame inattendue' {Anatomie Philosophique, p. 481) : and elsewhere describes it as a 

 " disposition veritablement trfes singuliere, et que le manque absolu du cou et une combinaison des pieces 

 du sternum avec celles de la tete pouvoicut seules rendre possible." — Annalesdu Museum, i,\, p. 3()1. A due 

 appreciation of the law of vegetative uniformity or repetition, and of the ratio of its prevalence and power to 

 the grade of organization of the species, was, perhaps, essential in order to discern the true signification of 

 the connexion of the scapular arch in fishes. 



f See my Discourse ' On the Nature of Limbs,' 8vo, Van Voorst, 1849, pp. 64-/0. 



