SKELETON. 



659 



that vertebral series (G, H, I, K, L, M, N) is still 

 uninterrupted as it passes from dorsal ver- 

 tebras (P), through cervical vertebrae, to cra- 

 nial vertebra? (F, E, D, c, B, A). Tims we find 

 that vertebral series persists continuously, 

 while costal series is interrupted by the cer- 

 vical hiatus happening between the maxilla 

 above and the thoracic costa? below. This 

 hiatus is caused by the degradation of costal 

 quantity simply, for we still see that rudi- 

 mentary ribs (g, h, i, k, /, m, H) are developed 

 upon each of the cervical vertebras. If the 

 original plus ribs of the cervical vertebra? 

 still persisted at the lines qqq, for them as 

 the plus ribs (pp*) do for the dorsal ver- 

 tebrae, then we should have the maxilla hold- 

 ing serial continuous order with the thoracic 

 ribs, in which case it could scarcely be doubted 

 that the maxilla? were structural homologues 

 of the costae elsewhere. But in this occur- 

 rence of cervical hiatus, which results by the 

 metamorphosis of that plus costal quantity 

 which I consider to be originally proper to 

 the cervical vertebrae, we have the facial ap- 

 paratus now disconnected from the thoracic 

 apparatus ; and the only structural entity 

 which at present relates the maxilla above to 

 the costae below is the hyoid apparatus 

 (f*,g*, h*,l*, k*). Hence this latter structure 

 can come of no other source than cervical 

 original costal quantity under metamorphosis. 



The idea of the plus costal quantity, which 

 we now know to be lost at the cervix, is 

 equal to the idea of the same quantity pre- 

 sent ; and hence, when I say that they are the 

 plus ribs which are lost to cervical vertebrae, 

 it is as strong an idea as if I still viewed them 

 persisting at the lines q q q. If these cervical 

 plus ribs still persisted, they would leave no 

 doubt that the maxillae are of costal origin. 

 Indeed the maxillae, as they at present stand, 

 prove a much stronger resemblance to ribs 

 than cranial vertebrae do to spinal vertebrae ; 

 and if we see little reason to doubt the iden- 

 tity between the latter structures, there is, as 

 it seems to me, even still less reason to doubt 

 the homology or correspondence between the 

 two former. 



In Jig. 481. I have indicated the number of 

 those vertebral forms which constitute the 

 human cranium, taking as my guide the in- 

 variable attendance of the costal structure 

 upon the vertebral structure, as well in the 

 head as in all other regions of the spinal 

 axis. The first dorsal vertebra (P) is attended 

 by the plus ribs (p p*), stretching over tho- 

 racic space from the back to the sternum. 

 All the cervical vertebrae (N, M, L, K, i, n, G) 

 are likewise attended by the minus costa? 

 (n,m,l,le,i,h,g). From these severally I 

 have produced lines to the hyoid apparatus, 

 and these lines, together with the hyoid 

 pieces, indicate thoracic costo-sternal quan- 

 tity, which metamorphosis has degraded down 

 to the quantities at present forming the cervi- 

 cal region. The intervals between the cervi- 

 cal lines of the original costa? are marked 

 (717) as corresponding with the intercostal 

 spaces. 



The atlas (G) supports the occipital or first 

 (reckoning from below) cranial vertebra. In 

 the atlas vertebra* may be recognised (g] the 

 vertebral end of its rib, which when pro- 

 duced through the line q joins g, the greater 

 cornu of the hyoid bone, to which latter the 

 body g* is attached ; this group of elementary 

 parts represents the debris of the archetypal 

 sterno-costo-vertebral quantity ; the atlas 

 stands in series with the other vertebra?, 

 while the inferior half of the hyoid bone 

 holds series with the tternum. The axis 

 vertebra (H), in the same way, corresponds to 

 the (//*) thyroid cartilage. The third cervical 

 vertebra (i) corresponds to the cricoid carti- 

 lage (i*). The fourth vertebra (K), the filth 

 (L), the sixth (M), point to the rings of the 

 trachea. The seventh vertebra (N) stands 

 opposite to the clavicle (?z), which I regard as 

 the costa of that vertebra. 



The first or occipital costo-vertebral quan- 

 tity of the head consists of (F) the centrum 

 and the pieces V"", 2, 3, which form the 

 neural arch and spine. The rib and sternum 

 or costo-sternal quantity of this vertebra is re- 

 presented by the styloid process (/), which, 

 when produced in a line to (/*) the upper 

 half of the hyoid body with its lesser cornu, 

 completes this group of elemental parts.-f- 



The seconder petrosal costo-vertebral quan- 

 tity of the head consists of (E) the centrum 

 and the parts I"'", 2, answering to the neural 

 arch and spine ; the costo-sternal quantity of 

 this vertebra is represented by the tympanic 

 bone (e) coiled upon itself, and enclosing 

 within its circle the auditory ossicles. The 

 tympanic bone, together with the auditory 

 ossicles, may be regarded as costo-sternal 

 quantity, specially modified in subservience to 

 the special sense of hearing, j 



The third or temporal costo-vertebral quan- 

 tity of the head has no part corresponding to 

 the body at D ; but the neural arch and bicleft 

 spine of this segment of the skull are repre- 

 sented by the parts I"", 2. The costo-sternal 

 quantity of this vertebra is represented by the 

 lower maxilla (d) articulating like a rib with 

 the glcnoid cavity (Y/). 



Thejmtrt/i or post sphenoid-costo-vertebral 

 quantity consists of (c) the centrum and the 

 parts I'", 2, answering to the neural arch and 

 spine. The costo-sternal quantity of this 

 vertebra is represented by the zygoma (c, c~) 

 and upper maxilla (c 1 *). 



* Professor Owen refers the clavicles to the atlas 

 vertebra, and considers them as forming the Iwiiiul 

 inverted arch of this vertebra. See " Homolo- 

 gies," &c. 



t The scapulary limbs are referred by Professor 

 Owen to his occipital vertebra, of which he con-i- 

 drrs the scapula; to be the ribs, and tiic iv>t of these. 



members to represent what he terms the "diverfiun- 

 i )) *^ 



appendages. 



J Professor O\ven dues not regard the petrous 

 bone as a part of a cranial vertebra, hut he calls it a 

 " sense capsule," and refers it to the splanchno 

 skeleton. 



The styloid process is regarded by Professor 

 Owen as the rib of his parietal vertebra. 

 u u 2 



