ON THE VERTEBRATE SKELETON. 287 



might reply, to neither. And such, doubtless, would be the matter-of-fact 

 answer most congenial to the character of mind which would limit its views 

 to the specialities of the ribs as parts independent of any ideal archetype, or 

 be unable or unwilling to push the consideration of their connections beyond 

 the purposes apparently subserved thereby. A second anatomist might see 

 in the more constant articulation of the costal tubercle with the transverse 

 process, a character which would incline the balance in favour of the vertebra 

 to which the transverse process belonged. A third anatomist might extend 

 his comparisons to other ribs and centrums, and finding the lower centrum 

 obtaining by degrees a greater proportion of the head of the rib, until the 

 first and last ribs respectively wholly articulated to the centrum answering to 

 the lower one in the case of the hypothetically detached sixth pair, he would 

 conclude that such pair of ribs belonged essentially to the lower and not 

 to the upper supporting centrum, and he would count accordingly such 

 lower centrum with its neural arch, as the sixth of those vertebrae which are 

 characterized as supporting ribs. The anthropotomist, in fact, in so counting 

 and defining the dorsal vertebrae and ribs, admits unconsciously perhaps, an 

 important principle in general homology, which pursued to its legitimate 

 consequences and further applied, demonstrates that the scapula is the modi- 

 fied rib of that centrum and neural arch which he calls the ' occipital bone,' 

 and that the change of place which chiefly masks that relation (for a very 

 elementary acquaintance with comparative anatomy shows how little mere 

 form and proportion affect the homological characters of bones) differs only 

 in extent and not in kind from the modification which makes a minor amount 

 of comparative observation requisite in order to determine the relation of the 

 shifted sixth lib to its proper centrum. 



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

 comparatively well-developed and permanently distinct ribs of all the cervical 

 vertebrae prove the scapular arch to belong to none of those segments, and, 

 if it be wanting 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*. " 



With these views of the general homology of the scapulo-coracoid arch, 

 the embryologist will observe with less surprise its constant appearance in 

 the first instance close to the occiput, and its equally constant primitive ver- 

 tical position ; however far back it may be subsequently removed, or to 

 whatever extent it may be rotated, in the same progress to maturity, out of 

 its original parallel direction with the more normal pleurapophyses. 



Returning to the study of the crocodile's skull in reference to the verte- 

 brate archetype, if we proceed to dislocate the next segment in advance of 

 the occipital, we bring away in connection with the long base-bone, 5 and 9, 

 fig. 22, the bones connected by the double lines N 11, N in, and by the 



* Geoffroy St. Hilaire selected the opercular and subopercular bones to form the inverted 

 arch of his seventh (occipital) cranial vertebra (Table III. and note 11), and took no account 

 of the instructive natural connections 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 ' amalganie inattendue ' (Anatomie Philo- 

 sophique, p. 481) ; and elsewhere describes it as a " disposition veritablement tres singuliere, 

 et que le manque absolu de cou et une combinaison des pieces du sternum avec celles de la 

 tete pouvoient seules rendre possible." — Annales du Museum, ix. p. 361. A due appre- 

 ciation 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, might have enabled him to discern 

 the true signification of the connection of the scapular arch in fishes. 



